After winning only one of their first six games, the 49ers and backup Troy Smith turned it on in the fourth quarter yesterday to beat the reeling Denver Broncos, 24-16, in the NFL’s fourth regular-season game in London.

Smith, the 2006 Heisman Trophy winner from Ohio State, found out only a few days earlier he was going to start at Wembley Stadium because Alex Smith was diagnosed with a separated shoulder. And he struggled in the first half, completing 4 of 9 passes for 37 yards.

He finished with 196 yards on 12-of-19 passing.

“Even though we missed some things early on, I think the rhythm was put in place to make some plays later on,’’ said Smith, who was making the third start of his career. “You have to be able to keep your head down and keep even-keeled as a quarterback.’’

Smith completed three long passes in the fourth quarter to get the offense going. Trailing, 10-3, Smith tied the score by rushing for a 1-yard touchdown after completing back-to-back passes to Delanie Walker, the first for 27 yards and the second for 38 following a scramble.

Less than five minutes later, Smith threw a 28-yard touchdown pass to Michael Crabtree to put San Francisco (2-6) ahead, 17-10. Frank Gore scored another TD with 3:47 to go, running in from the 3.

The Broncos (2-6) got their first touchdown in the third quarter when Tim Tebow ran in from a yard after Kyle Orton connected with Brandon Lloyd for 71 yards. Orton pulled the Broncos within a score with 2:19 to go in the game, hitting Lloyd for a 1-yard touchdown. But Matt Prater shanked the extra point attempt.

Although it rained in London for much of the day, it was dry during the game. As the home team, the 49ers were able to distribute flags to the 83,941 fans, who were dressed in myriad NFL colors. But the majority were cheering for San Francisco, making it feel “like a home game,’’ according to cornerback Shawntae Spencer.

“I wish I could play a game over here every year,’’ 49ers linebacker Takeo Spikes said.

Tony Romo could only watch from the sideline, his left arm in a sling because of a broken collarbone, as the Cowboys (1-6) went from striking distance to blowout very quickly. Dallas was within 14-3 and inside the 1-yard line just before halftime when Romo’s replacement, Jon Kitna, turned right and Marion Barber went left. There was a handoff, a collision, and a goal-line stand for Jacksonville. Garrard opened the second half with TDs on his first two drives, making it 28-3.

The Jaguars (4-4) were coming off losses by 22 and 27 points, with Garrard having missed the last game recovering from a concussion. Yesterday, he completed his first 12 passes and finished 17 of 21 for 260 yards. Even with three sacks and a lost fumble his rating was 157.8; perfect is 158.3.

Jacksonville’s defense intercepted four passes — as many as it had all season. The first three bounced off the hands of a Cowboys receiver. Kitna was 34 of 49 for 379 yards, with one TD.

Stafford, playing for the first time since Week 1 when his right shoulder was separated, was 26 of 45 for 212 yards with an interception. Johnson had nine catches for 101 yards and a career-high three scores.

Redskins quarterback Donovan McNabb was benched for the final two possessions. Coach Mike Shanahan inserted Rex Grossman to run the team’s two-minute offense, and the move backfired. Grossman fumbled on his first play, and Suh scooped up the ball and returned it 17 yards for a TD.

Washington had a 25-20 lead with 4:40 left when Alphonso Smith stepped in front of McNabb’s pass at the Redskins’ 41 to set up the go-ahead TD. McNabb was 17 of 30 for 210 yards.

The Bucs (5-2) moved into a tie with idle Atlanta for first place in the NFC South. Josh Freeman’s 53-yard pass to rookie Arrelious Benn set up LaGarrette Blount’s 1-yard run for what proved to be the winning score with 5:13 left. Freeman now has six fourth-quarter comebacks in 16 career starts. Blount, the rookie from Oregon, rushed for 120 yards and two TDs.

Derek Anderson, who replaced Max Hall after the Cardinals rookie had two early interceptions returned for scores, rallied Arizona (3-4) from a 17-point deficit to take a 35-31 lead with 9:41 to play.

On the go-ahead drive, Freeman converted on a fourth-and-1 run, and two plays later Blount scored. After Tampa Bay later had a 53-yard field goal blocked, giving the Cardinals a chance to tie, Talib picked off his second pass at the Buccaneers’ 3 with 2:15 remaining.

Succop had a chance to win it with 3:38 to go in OT, but his 39-yard attempt hooked left at the last instant. Buffalo’s Rian Lindell hit what would have been a 53-yard winner earlier in overtime but the kick was nullified because the Chiefs (5-2) had called time out. Forced to do it again, Lindell kicked a wobbler that hit the right upright.

The Bills (0-7), who lost in overtime to Baltimore the week before, are off to the third-worst start in franchise history. Ryan Fitzpatrick’s 4-yard TD pass to Steve Johnson on fourth and goal tied the game at 10-10 with 2:18 left in regulation.

After rolling up 59 points and 508 yards against Denver last weekend, Oakland gained 545 yards, marking the first time in franchise history it put together consecutive 500-yard performances. Darren McFadden ran for 111 yards, his fourth 100-yard game this season, and Darrius Heyward-Bey had a career-high 105 yards receiving.

The Seahawks didn’t pick up a first down until more than 27 minutes into the game and finished with a mere 47 yards on the ground. Olindo Mare kicked a 47-yard field goal with 8:57 remaining, but the Raiders still finished with their fewest points allowed since shutting out Kansas City in the final game of the 2002 season.

Bradford was 25 of 32 for 191 yards and no interceptions. The Panthers’ Matt Moore was picked off three times.