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ORCHARD PARK, N.Y. -- Tim Tebow picked a terrible time to run out of fourth-quarter comebacks.

Rather than inspiring the Denver Broncos to another dramatic rally, the quarterback sealed the most dreadful performance of his two-year career by throwing three interceptions and fumbling once -- all in the second half and two returned for touchdowns 18 seconds apart -- in a 40-14 loss to the Buffalo Bills on Saturday.

It happened as the Broncos (8-7) had a chance to inch closer to clinching their first playoff berth in six years, and against a Bills team that was coming off seven straight losses and had little to play for.

"My confidence is just fine," Tebow said. "I have to do a better job of not giving them opportunities. I tried to make something happen, and I tried to force it."

Denver coach John Fox hasn't lost faith in Tebow.

"I just think a couple of misreads," Fox said.

And no, he gave no thought of pulling Tebow at any point during a second half in which four of the Broncos' final six possessions ended with interceptions.

On the bright side, Denver's not done yet, despite falling into a tie with Oakland atop the AFC West. Denver closes its season by hosting the Kansas City Chiefs next week, and still holds the tiebreaker edge over the Raiders.

"Everything is still on the table," Tebow said. "We have to go and execute and play a little better. Hopefully, we can get in the tournament."

Tebow finished 13 of 30 for 185 yards with a 17-yard touchdown pass to Daniel Fells. He added 34 yards rushing, and scored on a 1-yard plunge.

He initially was credited with four interceptions, but at midweek, one was changed by the NFL to a fumble.

That wasn't nearly good enough for a player who entered the game best known for engineering five fourth-quarter comebacks this season.

The Bills (6-9) made sure he never got in position for a sixth in coming away with a win in their home finale.

Safety Jairus Byrd and linebacker Spencer Johnson scored on interception returns 18 seconds apart midway through the fourth quarter. C.J. Spiller rushed for a career-best 111 yards and a touchdown, and Leodis McKelvin scored on an 80-yard punt return.

"It's special," Johnson said. "We had a monkey on our back for a long time."

Added safety George Wilson: "It's a great reward for the resilience, commitment and dedication."

The Bills' three interceptions was one more than they managed in their previous seven games. They have returned five interceptions for touchdowns to set a single-season franchise record.

If the game wasn't over with 8:03 left when Byrd jumped in front of Tebow's pass intended for Eric Decker up the left hash mark and returned it 37 yards for a touchdown, then it certainly was decided on the Broncos' next play from scrimmage.

Tebow was flushed from the pocket and was scrambling to his left when linebacker Chris Kelsay dived from behind and batted the ball out of the quarterback's hand. The ball flew into the air and landed in the hands of Johnson, who ran it in from 17 yards.

Kelsay, the longest-serving member of the defense, had two sacks and led the team with nine tackles.

"We've lost seven games in a row. It wears on you," Kelsay said. "We got rewarded. We came together and we executed."

After weeks of assertive defense, the Broncos gave up 40 points for a second straight game -- though Tebow's giveaways certainly didn't help. And yet Denver allowed 160 yards rushing and 351 yards in all to a banged-up Bills offense that was averaging 14.2 points and 314.7 yards during its seven-game skid.

While Tebow was struggling, Bills quarterback Ryan Fitzpatrick enjoyed his most efficient game in two months by going 15 of 27 for 196 yards with no interceptions. Fitzpatrick entered the game taking plenty of heat during the seven-game skid, in which he threw eight touchdowns versus 12 interceptions.

Dave Rayner shook off two missed field-goal attempts -- and a booing crowd -- to hit his final four, all from within 29 yards.

"I'm glad that Coach stuck with me," Rayner said. "I'm glad that we got opportunities, because I never want to leave a game going oh-fer."

Except for scoring touchdowns on their first possession of each half, nothing went right for the Broncos.

They went nowhere in the first half after Tebow capped a 73-yard opening drive with a 1-yard run. Denver managed just 21 yards and no first downs on its final six possessions, including a kneel-down in the final seconds.

They finished converting just two of 13 third-down chances and Tebow had four of his final six drives end with interceptions.

Game notes

After McKelvin scored, Denver's Eddie Royal returned the ensuing kickoff 94 yards for a touchdown, but it was negated by a block in the back penalty against Dante Rosario. ... Broncos RB Willis McGahee had 64 yards rushing to give him 1,054 this season. He became the second NFL player to reach 1,000 yards rushing with three teams. He previously did it with Buffalo and Baltimore. Ricky Watters rushed for 1,000 yards with San Francisco, Philadelphia and Seattle. ... The Bills finished 5-3 at home (including a win over Washington at Toronto), matching their best record since going 5-3 in 2004.