KANSAS CITY, Mo. - The Chiefs and Allen Bailey agreed to a four-year, $25 million contract extension Saturday that could keep the defensive end playing in Kansas City through the 2018 season.

The former third-round pick is guaranteed $15 million and will receive a $10 million signing bonus, a person familiar with the deal told The Associated Press. The person spoke on condition of anonymity because the Chiefs did not announce the terms of the extension.

Pro Football Talk was the first to report that a deal was in place.

"We are happy that we were able to reach an agreement to keep Allen in Kansas City," general manager John Dorsey said in a statement Saturday. "He has developed into a good football player and a key member of our defence."

The 25-year-old Bailey has had a breakout season for the Chiefs, starting all nine games and establishing a career-high four sacks. He's helped the Chiefs deal with season-ending injuries to starters Derrick Johnson and Mike DeVito and still become one of the NFL's best defences.

The Chiefs (6-3), winners of six of their past seven, ranked first in the league against the pass and seventh in total defence heading into Sunday's game against Seattle.

"Allen's had a really good year and he made a big jump a year ago, I thought, in football and knowing what's going on," Chiefs defensive co-ordinator Bob Suttons said recently. "He's obviously a very gifted guy athletically. Like I say, he could play 80 plays every week and never get tired. He and (Dontari) Poe are very similar in that way."

Bailey played mostly in sub packages his first three seasons out of Miami, but he was thrust into a bigger role this season. His mammoth size — 6-foot-3, 280 pounds — and uncanny speed make him a dangerous pass rusher on the defensive line, and gives opposing offences another player to worry about along with talented outside linebackers Justin Houston and Tamba Hali.

Bailey is on pace for nearly eight sacks this season, which would be the most for a Chiefs defensive lineman since Jared Allen had 15 1/2 sacks during the 2007 season.

He also forms a formidable front with Pro Bowl defensive tackle Dontari Poe.

"The arrow's up," Sutton said. "Got really good athleticism. One thing that's really great for us is those two inside guys, they can make a lot of plays chasing things down and that doesn't happen a lot.

"A lot of times you're not fortunate enough to have that kind of player. You might have a big sturdy guy in there that maybe can't make the plays outside. These two guys can chase screen plays down, wide plays and they really help your defence."

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