The Kansas City Chiefs already have made plenty of bold moves this offseason.

They made another one on Thursday.

The Chiefs agreed to terms with cornerback Sean Smith on a three-year deal, helping to shore up their secondary opposite cornerback Brandon Flowers. The move also gave the Chiefs the type of lockdown defender they needed to deal with a bevy of talented wide receivers in the AFC West.

Smith was widely considered among the best cornerbacks available in free agency.

He’s spent his entire career with the Miami Dolphins, starting every game each of the past two years, and has 177 tackles and five interceptions in his four-year career.

The move was made possible in part because the Chiefs cleared salary cap space Thursday by releasing Matt Cassel. The quarterback had two years left on his six-year, $63 million contract.

“There are still a few holes left. There’s no doubt about it,” new Chiefs general manager John Dorsey said Wednesday, when asked to assess his roster. “It’s how you go and attack that. But at the end of the day, players we acquire will be able to fill all the holes we need.”

The Chiefs had two of the best cornerbacks in the AFC two years ago in Flowers and Brandon Carr, but they allowed Carr to slip away in free agency prior to last season.

They signed Stanford Routt as his replacement, but he never quite fit in and was released midway through the year. Kansas City played the rest of the way with Javier Arenas, an undersized defensive back better suited to the nickel, and second-year pro Jalil Brown as the starters.

Kansas City added depth earlier in the week by signing a three-year deal with cornerback Dunta Robinson, who has spent the past nine seasons with Houston and Atlanta, but evidently was still in the market for a cornerback who is just coming into his prime.

The Chiefs found it in Smith, a former second-round draft pick out of Utah.

He started every game as a rookie, but ran into trouble in 2010 — he was benched at one point for violating team rules, and lost his starting job to Jason Allen. Smith admitted that he wasn’t taking his job seriously, rededicated himself and became a standout in the Dolphins secondary.

He made a career-high 59 tackles and two picks last season.

The move for Smith came one day after the AFC West-rival Denver Broncos agreed to terms with wide receiver Wes Walker on a two-year deal to provide Peyton Manning with another pass-catching option alongside Demaryius Thomas and Eric Decker.

The Chiefs and Broncos have been two of the biggest movers in free agency, with the Chiefs trying to rebuild under Dorsey and new coach Andy Reid after finishing 2-14 last season.

Already, they’ve revamped their offense by trading for quarterback Alex Smith and signing wide receiver Donnie Avery, tight end Anthony Fasano and backup quarterback Alex Smith.

They’ve also added former Vikings safety Husain Abdullah and former Jets defensive tackle Mike DeVito to a defense that landed four players in the Pro Bowl last season.

“If you take one common denominator with the free agents brought in so far, there’s a certain grit and toughness about them,” Reid said this week. “I welcome that to our football team. I think our locker room will welcome that.”

— Associated Press —

The Kansas City Chiefs announced on Thursday that the club has released quarterback Matt Cassel.

Cassel (6-4, 230) played in 48 games (47 starts) with Kansas City (2009-12). In four seasons with the club, he accumulated 9,549 yards on 854 completions (54.7 pct.) with 59 touchdowns and 44 interceptions for a 77.5 rating. Prior to joining the Chiefs, Cassel spent four seasons in New England (2005-08). His career numbers include 1,203 completions on 2,044 attempts (58.9%) for 13,495 yards with 82 touchdowns and 57 interceptions for an 80.4 rating.

Cassel was originally acquired by the Chiefs in a 2009 trade that brought him along with linebacker Mike Vrabel to Kansas City from New England in exchange for a second-round pick in the 2009 NFL Draft. The Chatsworth, Calif., native, entered the NFL as a seventh-round pick (230th overall) of the Patriots in the 2005 NFL Draft. He played collegiately at USC and prepped at Chatsworth High School in Chatsworth, Calif.

— Chiefs Media Relations —

The Kansas City Chiefs finally have their new quarterback.

The Chiefs officially traded for Alex Smith on Tuesday, the first day of the new league year – and nearly two weeks after the San Francisco 49ers agreed to the deal. All that’s left is for Smith to pass a physical and the paperwork to be filed with the league.

That business is expected to be finished Wednesday.

The 49ers will receive the Chiefs’ second-round pick, 34th overall, in this year’s draft and a conditional pick in next year’s draft, a person familiar with the terms told The Associated Press. The person spoke on condition of anonymity because the terms were not disclosed.

Kansas City also agreed Tuesday to a four-year, $16 million deal with former Dolphins tight end Anthony Fasano, a three-year, $12.6 million contract with defensive tackle Mike DeVito, and a three-year deal with former Saints backup quarterback Chase Daniel.

The moves continue what’s been a busy offseason for the Chiefs under new general manager John Dorsey and coach Andy Reid. Last week, they signed wide receiver Dwayne Bowe to a five-year, $54 million deal, punter Dustin Colquitt to a five-year, $18.75 million deal, and placed the franchise tag on left tackle Branden Albert, promising him $9.83 million for the 2013 season.

Dorsey and Reid were not available to comment on Tuesday’s moves.

“Part of this movement was from a philosophical belief that has been ingrained in me,” Dorsey told AP in an interview last week, when asked about how quickly he’s hit the ground running.

“Winning organizations,” he said, “do moves like this.”

Under the three-year contract he signed last March, Smith is guaranteed $8.5 million for the 2013 season, though it’s possible the Chiefs will attempt to sign him to a new deal.

The Chiefs’ big spending was made possible by carving out space under the salary cap.

The new regime has released right tackle Eric Winston, wide receiver Steve Breaston and tight end Kevin Boss, and restructured the mammoth contract of defensive end Tyson Jackson. The Chiefs are also expected to release incumbent quarterback Matt Cassel in the coming days.

The poor play of Cassel, who has two years left on a six-year, $63 million deal, is one of the reasons the Chiefs went 2-14 last year and have the No. 1 pick in the NFL draft, and why the new front office targeted Smith in the days and weeks after their arrival.

Smith had eight up-and-down years with the 49ers, but thrived under coach Jim Harbaugh. He went 13-3 as the starter two years ago, and was 6-2 at the midway point this past season, completing 18 of 19 passes with three TDs in a Monday night win over Arizona on Oct. 29.

He then sustained a concussion in the second quarter of a 24-24 tie against St. Louis on Nov. 11, saying later he threw a touchdown pass with blurry vision. Smith sat out the next game, Colin Kaepernick dazzled in his debut as an NFL starter – and Smith never started again.

Kaepernick led the 49ers to the Super Bowl and Smith became expendable.

Smith approached the delicate situation with grace, and said in response to questions about it, “I feel like the only thing I did to lose my job was get a concussion.”

“We would like to thank Alex for his contributions to the 49ers organization over the past eight years,” 49ers GM Trent Baalke said in a statement Tuesday. “He is a true professional who represented the 49ers with class on and off the field.”

Smith will try to settle a Chiefs quarterback situation that’s been shaky for years.

After leading Kansas City to the playoffs in 2010, Cassel struggled to perform at the same level. He injured a hand in 2011, forcing Tyler Palko and Kyle Orton to finish out the year, and a head injury this past season cleared the way for Brady Quinn to step in.

Quinn fared little better in eight games and became a free agent.

The only other quarterbacks on the Chiefs’ roster were former fifth-round draft pick Ricky Stanzi and journeyman Alex Tanney, so Dorsey and Reid targeted Daniel to provide some depth.

Daniel has spent the past three years backing up Drew Brees in New Orleans.

Fasano, who spent the past five seasons with Miami, has proven to be a solid pass-catching tight end. He had 41 catches for 332 yards and five touchdowns last season, and has 205 catches for 2,373 yards and 24 touchdowns in 108 career games.

DeVito, a run-stuffing defensive tackle, started 15 games for the Jets last season. He’ll be expected to solidify a defensive line that struggled to stop the run last season.

— Associated Press —