Tom Brady took off for the end zone and dived for the pylon, taking a helmet in the back as his body sailed over the goal line.
The ball stayed out, but it didn't matter. The reigning Super Bowl MVP carried it in for a score on the next play, reaching over the line to convert in a way Kansas City couldn't Saturday.
Brady threw for two touchdowns to Rob Gronkowski and sneaked for another, and the defending Super Bowl champions reached their fifth straight AFC title game with a 27-20 victory over the Chiefs.
New England (13-4) will meet the winner of Sunday's game between the Pittsburgh Steelers and the Denver Broncos for a spot in Super Bowl 50. The Patriots are trying to become the first team to win back-to-back NFL titles since they did it in 2003-04.
"It's pretty special to get back to another AFC championship game," said Brady, who will play in his 10th conference title game. "It's pretty cool. It's hard to do, man. You've got to grind throughout the entire year. There's only four teams playing next week and we're one of them. That game means a lot."
After spending the last two weeks recovering from knee and back injuries, Gronkowski caught seven passes for 83 yards, including touchdowns from 8 and 16 yards out. Gronkowski also recovered an onside kick after Kansas City cut the deficit to 27-20 with just over one minute left.
Julian Edelman returned from a broken foot to catch 10 passes for 100 yards for New England. Danny Amendola had two catches for 18 yards.
"It's just great to have those guys back," Gronkowski said. "They're hard workers, they're great players. The chemistry was clicking tonight."
Alex Smith completed 29 of 50 passes for 246 yards and one touchdown for Kansas City (12-6). The Chiefs had won 11 consecutive games, including a 30-0 victory over Houston in the wild-card round last week for their first playoff victory since 1993.
Brady led New England to a score on the opening drive, throwing 11 straight passes and completing eight — the last an 8-yard score to Gronkowski. The Chiefs then made it to the Patriots 16, but settled for a field goal.
After trading punts twice, the Patriots started on their when punt returner Danny Amendola was flagged for a helmet-first hit to coverage man Jamell Fleming. The drive was in danger of stalling at the Kansas City 35 when Chiefs linebacker Dezman Moses hit Brady late and was called for roughing the passer.
The stadium erupted in cheers of "Brady!" — just as it had four months ago when the four-time Super Bowl champion returned from his looming "Deflategate" suspension to play in the season opener.
Four plays later, unable to find an open receiver, Brady sprinted — sort of — for the corner of the end zone. The Chiefs managed to keep him out, but only for one more play. On the next snap, Brady leaned forward and reached into the end zone to make it 14-3.
"I thought I could try to make it. We were close. Not close enough, but we got in on the next play," said Brady, who shrugged off the two big hits on that drive. "It's football season, so there's bumps and bruises, but you've got to fight through those."
Patriots defensive lineman Chandler Jones forced Knile Davis' fumble on the Chiefs' first possession of the second half, then Brady added another touchdown pass to Gronkowski to make it 21-6.
Smith had the Chiefs into New England territory on their first six possessions, but they managed just six points before he hit Albert Wilson on a 10-yard pass that made it 21-13.
Notes: Jones started the game, six days after he wandered to the local police station, shirtless and confused. Police said his house reeked of burnt marijuana. ... The Patriots are 18-4 all-time in the playoffs at Gillette Stadium. ... Jon Bon Jovi, a friend of Patriots coach Bill Belichick, was in the owner's box and led the stadium in a sing-along of his band's hit song "Livin' on a Prayer." ... Belichick reached the conference title game for the 10th time, tied with Tom Landry for most all-time.