"That's got to be one of the biggest hits he's gotten for us," San Diego manager Bud Black said of Forsythe, who singled on a 1-2 count.
Especially considering the circumstances where the Padres (63-74) lost a game in Colorado on Sunday in which they had scored 10 runs and had 20 hits and then, on Monday, lost a 4-3 game in 11 innings to the Dodgers (73-64).
"This feels great," said Padres rookie reliever Tommy Layne, who picked up his first Major League win by striking out Adrian Gonzalez, Matt Kemp and Hanley Ramirez in the 10th. "You look at today's game and everyone had an important role, everyone did their job.
"We needed that."
Cameron Maybin started the 11th inning with a single off John Ely (0-1) and moved to third base on an infield hit by Everth Cabrera on a bunt and a throwing error on the play by Luis Cruz. After pinch-hitter Alexi Amarista grounded out, Forsythe singled through a drawn-in infield.
Chase Headley followed with an RBI single to give the Padres a three-run lead.
"You've got to give a lot of credit to the Padres," Dodgers starter Clayton Kershaw said. "They battled me all night. They put some great at-bats together all night. That team is playing really well right now, swinging the bats well, pitching well. Those are the games we have to win."
Shane Victorino had a run-scoring single in the bottom of the seventh inning and Gonzalez followed with a sacrifice fly as the Dodgers took a 3-1 lead.
But the Padres came back in the eighth inning and tied it when Yasmani Grandal hit a two-run home run off reliever Matt Guerrier.
Kershaw allowed one run on five hits over seven innings with three walks and nine strikeouts. He got nine ground-ball outs.
San Diego pitcher Eric Stults allowed one run on seven hits in six innings. He walked one, struck out one and got 11 ground-ball outs.
"He's got a great changeup and he kept us off-balance all night. He did a really good job," Kershaw said of Stults.
The Padres struck first -- and fast -- as leadoff hitter Chris Denorfia jumped on a first-pitch fastball from Kershaw, sending it over the fence in left field for his sixth home run of the season.
The Dodgers tied the score in the second inning on Andre Ethier's 17th home run of the season, a solo shot to right field. For Ethier, it was his fifth home run against the Padres this season and the 1,000th hit of his career.
The Padres had runners on second and third with one out in the fourth inning but couldn't score. Then in the sixth inning, Carlos Quentin doubled and moved to third base on a ground ball. But Kershaw got Yonder Alonso to ground out and then struck out Maybin to end the inning.
In the fourth inning, Alonso doubled off Kershaw, his 33rd double of the season. That ties him for the most doubles by a Padres rookie since Benito Santiago reached that mark in 1987.
Stults allowed the first two hitters of the sixth inning to reach base but survived a first-and-third jam with no outs by getting the next three hitters out to preserve a 1-1 tie.
The series concludes at 7:10 p.m. PT on Wednesday.