The fleet wide receiver is happy in his new home with the San Francisco 49ers, another championship contender that’s making better use of Manningham than the Giants ever did.

It’s a different situation for Brandon Jacobs. Now healthy after a preseason knee injury, Jacobs has yet to play for the 49ers this season.

This could be the week Jacobs finally makes an impact as he and Manningham eagerly anticipate their first game against their former team when the Giants come to San Francisco on Sunday for a rematch of January’s NFC championship game.

Manningham already has made his mark with a San Francisco offense that set a franchise record by gaining 621 yards during last week’s 45-3 rout of the Buffalo Bills.

The fifth-year veteran has worked his way into the starting lineup ahead of newcomer Randy Moss and is third on the team with 19 receptions, including at least three catches in each of San Francisco’s five games. He also has rushed for 57 yards on two reverses after rushing for minus-10 yards during his career with the Giants.

“I’ve had as many (carries) in four months here as in four years in New York,” Manningham said Thursday. “I feel like they’re putting me in a good position to move the chains and make plays. And it’s not like I left a good team and went to a bad team.”

Manningham played a key role in the Giants’ Super Bowl run last year, catching a 17-yard pass against the 49ers for New York’s final touchdown during a 20-17 overtime victory for the NFC title. He also had a 38-yard reception late in the fourth quarter to spark New York’s winning touchdown drive against New England in the Super Bowl.

Manningham made an impressive play on the latter catch, tip-toeing along the sidelines for what 49ers offensive coordinator Greg Roman called, “one of the biggest plays in Super Bowl history.”

Manningham has added an element of speed and shiftiness to a San Francisco passing game that is improved by his presence. He completely turned around a Buffalo defender last week to get wide open in the end zone and catch a 10-yard pass from Alex Smith for Manningham’s first touchdown with the 49ers.

“Mario is an outstanding receiver, very fast, very good along the sideline,” New York coach Tom Coughlin said. “So you see what has transpired with his addition.”

It remains unclear whether the Giants will face Jacobs, a key player on two Super Bowl championship teams during his seven seasons in New York.

Jacobs started 48 games and rushed for 4,849 yards and 56 touchdowns with the Giants, who released him earlier this year when Jacobs declined to take a significant pay cut. He later signed a one-year, $1.575 million deal with San Francisco.

Jacobs had a strong training camp and appeared to be earning himself a role in San Francisco’s offense before suffering ligament damage in his left knee during an Aug. 18 exhibition game at Houston.

He has practiced without limitations for several weeks and expressed frustration that he did not play against the Bills. But on Thursday, Jacobs backed off comments he made earlier this week, saying his emotions are high with the Giants coming to town.

“The competitive nature in me, I just want to get out and play,” Jacobs said. “I’ve gone out and I’ve played in worse situations as far as injuries than I’m in now. I’m an emotional guy, and it’s going to be a good weekend for me. That’s all I can tell you.”

The 49ers haven’t needed help from Jacobs in the running game after rushing for 311 yards against the Bills, becoming the first team in NFL history to both rush and pass for 300 yards in the same game.

San Francisco ranks No. 1 in the NFL in rushing offense, but Jacobs expects the 49ers to get a stiff challenge from his former teammates.

“I know the guys over there,” Jacobs said. “I know it’s going to be war when they come in here. And I’m telling everybody they’re coming in to play football. That’s the way they’ve always been ever since I’ve been around and known them. But this team is going to play football as well, and this is a much better team than what they were last year. So it’s going to be a battle.”