The Kansas City Chiefs continued to spend to retain stars from their Super Bowl LIV championship team by agreeing to a four-year, $57.25 million contract extension with tight end Travis Kelce, a source told ESPN's Adam Schefter on Thursday.

The deal includes $28 million in guarantees, according to Schefter.

The average annual value will be slightly less than what San Francisco 49ers tight end George Kittle will receive after agreeing to a five-year, $75 million extension, sources confirmed to ESPN. Kelce and Kittle are widely considered the NFL's top players at the position.

The Chiefs announced Friday that they had signed Kelce to an extension but did not announce the terms.

Kelce had two years remaining on the five-year, $46 million deal he signed with the Chiefs in January 2016.

The Chiefs, who at one point early in the offseason had $177 of available space under the salary cap, last month signed quarterback Patrick Mahomes and defensive tackle Chris Jones to new contracts that could pay them as much as $600 million. Mahomes' 10-year extension could be worth about $500 million, which would be the largest contract in U.S. team sports history.

Mahomes reacted to the news of Kelce's agreement in a tweet.

6 MORE YEARS!!!!!!! https://t.co/6oCYYwajak pic.twitter.com/vE6QkfO7t9

— Patrick Mahomes II () August 13, 2020

Kelce, 30, has more than 1,000 receiving yards in each of the past four seasons, becoming the first tight end to achieve that. In 2019, he led all tight ends in receptions (97) and receiving yards (1,229) while posting five touchdowns in the regular season. He had 19 catches for 207 yards and four touchdowns in three postseason games.

Kelce's 1-yard touchdown catch in the fourth quarter of the Super Bowl started the Chiefs' rally from a 10-point deficit to a 31-20 victory over the 49ers.

The Chiefs in three years under general manager Brett Veach have signed many players to lucrative long-term contracts. Others include wide receivers Sammy Watkins and Tyreek Hill, defensive end Frank Clark and defensive back Tyrann Mathieu.

The Kelce contract is different in that all the other players were no older than 27 when they signed their deals.