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PITTSBURGH -- Until now, the Pittsburgh Steelers couldn't get Rashard Mendenhall going. The San Diego Chargers couldn't get him stopped. Mendenhall helped the Steelers run up a big lead, then made certain they didn't give it away with another fumbled fourth quarter.

Mendenhall surpassed his previous career totals with 165 yards rushing and two touchdowns, Ben Roethlisberger got fast-starting Pittsburgh going with his throwing and the Steelers opened a 28-point lead before holding on to beat the San Diego Chargers 38-28 on Sunday night.

Running back Mewelde Moore caught a touchdown pass and threw for another to Heath Miller on a goal-line play as the Steelers (2-2), beaten in the closing seconds by Chicago and Cincinnati the previous two weeks, built such a big lead that this bad fourth quarter didn't matter. Jeff Reed finished it off with a 46-yard field goal in the final minute.

"We haven't been able to finish, but this week we were able to," Roethlisberger said.

The Chargers (2-2), outgained nearly 4 to 1 until late in the third quarter and 497-251 overall, made an apparent blowout close as Philip Rivers threw touchdown passes of 30 yards to Antonio Gates and 13 yards to Chris Chambers and Jacob Hester scored on a 41-yard fumble return, all in the fourth quarter.

Mendenhall, a 2008 first-round pick who came in with 103 yards rushing and no touchdowns in his career, finally ran his way out of coach Mike Tomlin's doghouse while subbing for the injured Willie Parker (toe). Only a week ago, Mendenhall never got a single carry during a 23-20 loss in Cincinnati because Tomlin felt he didn't know the plays.

"I didn't have a chip on my shoulder," Mendenhall said. "He challenged me and it was a learning experience. I always had confidence in myself. I knew it was only a matter of time before I got an opportunity."

The first three plays showed how the AFC playoff rematch from a year ago would play out. Roethlisberger hit Santonio Holmes and Hines Ward for 15 yards each and rookie Mike Wallace for 35. Mendenhall then needed three carries to cover the final 14 yards for his first career touchdown with only 3:11 gone.

"Rashard really proved himself," tackle Max Starks said.

After San Diego went three and out, the Steelers put together a 75-yard drive that began with three Mendenhall runs but ended with Roethlisberger finding Ward for 15, Holmes for 11 and Moore twice for 23 yards, with the touchdown covering 19 yards.

"They came out and played about as well as they could play in the first half," Chargers coach Norv Turner said. "Obviously from our standpoint we'd like to think we could do some things to handle that. But we weren't able to respond the way I'd like to have seen us."

Roethlisberger was 26 of 33 for 333 yards and Ward had eight catches for 113 yards. Roethlisberger had the Steelers moving so well early, Tomlin allowed him to sneak for a first down on a fourth-and-1 from the Steelers' 30 on the drive that ended in Pittsburgh's third touchdown, on Mendenhall's 2-yard run.

"They had it in all phases," Chargers safety Clinton Hart said. "When you have it going like that, it's definitely hard to stop your opponent. They're world champions and they came out here to play."

Mendenhall, whose rookie season was ended a year ago by a fractured shoulder during this same fourth week of the season, came into the game with 103 yards rushing in seven career games. He had 100 yards by late in the third quarter and added a 32-yard run in the fourth quarter against the NFL's No. 26 rushing defense.

"I wanted people to see me and [see] who I am," Mendenhall said. "This was a time that I was able to do that, play a full game for the first time in my career."

Tomlin said, "I'm not taking any credit. I didn't rush for a single yard."

Not long after the Steelers made it 14-0 with 4:08 remaining in the first quarter, some NBC viewers might have been tempted to flip over to Pittsburgh-based medical drama "Three Rivers" on CBS -- if only because of the way the Chargers were struggling alongside those very same rivers.

It hardly was Rivers' fault. With no running game to support him -- LaDainian Tomlinson had 15 yards on 7 carries -- Rivers (21 of 36, 254 yards, 3 TDs) almost didn't have a chance to get his offense going until it was too late after throwing for 739 yards in his previous two games. The Steelers held the ball for nearly 23 minutes in the first half to San Diego's 7 minutes.

"We played a team that was 1-2 and super hungry and firing on all cylinders and they caught us on an off night," Rivers said. "We at least made it uncomfortable for these guys at the end."

The Chargers played in Heinz Field for the third time in 11 months -- as many appearances during that time as stadium tenant the University of Pittsburgh -- and lost for the third time. The Chargers are 0-14 in Pittsburgh during the regular season, although they have won there twice in the postseason.

San Diego was down 28-0 before a possession ended with anything but a punt, and the Chargers didn't advance inside the 20 until a drive that ended with Gates' 3-yard touchdown catch in the third.

San Diego cut it to 28-14 early in the fourth when the Steelers thought Stefan Logan was down on a punt return before he fumbled. He wasn't, and Hester ran into the end zone with no resistance. The Steelers unsuccessfully challenged the call.

Game notes

Pittsburgh has won its last eight home games, counting the postseason. ... San Diego lost for the first time in six games since 2002 against the Super Bowl winner of the previous season. ... Pittsburgh is 8-1 against San Diego since an AFC Championship Game loss in January 1995.