Molina's dramatics ended a gripping standoff.
"It was a little nerve-racking, as close games always are," said Giants starter Tim Lincecum, who struck out seven in six innings and bequeathed a 2-1 lead to the bullpen.
The Giants took that slender lead into the ninth inning, but closer Brian Wilson surrendered the tying run after walking leadoff batter Josh Bard -- which often launches a disastrous inning. Brad Hennessey (1-0) struck out three in two scoreless innings, but the Giants squandered opportunities in the ninth and 10th innings, moving runners into scoring position both times.
Molina ultimately rewarded the Giants by clobbering Cla Meredith's 1-2 slider into the left-field seats.
"He's so nasty on righties," Molina said of Meredith (0-1), who owned a 0.89 career ERA against the Giants entering the game. "I was just hoping he'd throw something middle-in and he did."
Having lurched through the season's first week, the Giants seized the chance to revel in this triumph by engulfing Molina at home plate.
Asked if this was how he envisioned his first game-winning homer, Molina replied, "It was way, way much better than I thought it would be. .... What's amazing for me was to see the joy, the happiness, the smiles."
In a way, Molina's feat wasn't a surprise. He established himself as the Giants' top hitter under pressure last year by hitting .338 with runners in scoring position and two outs. No wonder manager Bruce Bochy named Molina, who has three of the team's four homers this year, to be the Giants' cleanup hitter before the season started.
"Bengie's so clutch," Bochy said. "He's the guy you want up there when you need a big hit."
Molina insisted that he maintains the same approach regardless of the situation.
"I don't think about those things," said Molina, who opened the scoring with his second-inning homer off Padres starter Randy Wolf. "I told you guys from the get-go that I'm just a hitter. I'm not a fourth batter or a fifth batter or a seventh batter. All I'm doing is trying to hit the ball hard somewhere."
However, Molina was unrestrained in his praise of the Giants pitchers -- "That's more important for me that the pitching did well" -- and for good reason.
Left-hander Jack Taschner stranded a runner on second base in the seventh inning by retiring Adrian Gonzalez, who was 3-for-3 off him last season.
Tyler Walker marooned another Padre on second in the eighth inning by fanning Khalil Greene, a career .319 hitter at AT&T Park entering the game, and Scott Hairston, who tormented the Giants with seven home runs last year.
After Wilson blew his first save opportunity in two chances, Hennessey took over and rebounded from three subpar outings in which he recorded a 24.00 ERA and allowed opponents to hit .600 off him.
"He saved us tonight," Bochy said.
Earlier, Lincecum propelled the Giants with a typically energizing performance. He allowed two singles but struck out the side in the first inning, fanned Bard with two on and two outs to end the fourth inning and, with two Padres aboard in the sixth and a run in, struck out Hairston and retired Bard to finish his outing.
The Giants actually received a break in that sixth inning after the Padres loaded the bases with nobody out. Gonzalez and Kevin Kouzmanoff singled and Lincecum hit Jim Edmonds with a pitch. Greene lifted a fly to deep left field that Daniel Ortmeier dropped. Gonzalez scored but Kouzmanoff, believing Ortmeier had caught the ball, returned to second base and was tagged out. Had Kouzmanoff gone halfway toward third, as baserunners often do, he might have scored.