With the Cardinals clinging to a 4-3 lead in the sixth, Belt followed Angel Pagan's leadoff single with a ground ball past third base. That set up Emmanuel Burriss' sacrifice fly. One out later, Belt scored as Cardinals third baseman David Freese fielded pinch-hitter Aubrey Huff's ground ball and skipped his throw into the visitors' dugout -- one of three St. Louis errors that generated three unearned runs for the Giants.
Belt might have distracted Freese by crossing in front of him and obstructing his view of first base ever so briefly.
"He threw a screen there," Giants manager Bruce Bochy said, agreeing with this assessment.
One inning later, Belt lashed a more conventional extra-base hit, a line drive to right-center field that scored Buster Posey. The Giants ultimately loaded the bases and scored again on Charlie Culberson's fielder's-choice grounder.
Belt collected two extra-base hits in a game for only the third time in his 91-game Major League career. Mired in a 1-for-18 slump entering Thursday, he knew something had to change.
"I was being a little bit too aggressive and getting myself out a lot," he said. "I needed to pull back a little bit today and be a little more selective, and it worked out."
Belt has driven in runs in three consecutive starts, despite his hitting skid. This fits his profile as a ballplayer and fulfills what the Giants want from him.
"That's the hitter I've been my entire life, a person who drives in runs," said Belt, who accumulated 148 RBIs in 189 Minor League games from 2010-11. "That's my main priority. That's how I contribute to the team."
Belt, who has shuttled in and out of the lineup along with several other Giants, is the first to admit that he hasn't established a formidable presence at the plate.
"I don't feel perfect right now," he said. "Ideally, I'd like to be driving balls a little bit more. But for right now, you just kind of get your hits, especially when people are on base, and it ends up working out well."
Belt was complemented by shortstop Brandon Crawford, who made his debut batting second. After doubling and scoring in the first inning and lashing a two-run single in the second inning, Crawford likely will find himself No. 2 in the order again Friday when the Giants open a three-game Interleague series against Oakland.
"With guys in scoring position, I saw more fastballs than I think I probably would have seen hitting eighth," said Crawford, who ended a 16-game streak without a RBI.
The pitching beneficiary was Matt Cain (3-2), who earned an unusual victory. Plagued by insufficient offense too many times to count during his career, Cain yielded four runs in three innings but stifled St. Louis for the next three and put the Giants in position to win. The right-hander threw 74 pitches in the first three innings and 38 in his next three.
Said Posey, who recorded his second consecutive multiple-hit game, "We want to pick up every guy, regardless of who it is. But it feels good for us with Cain, because we know he lacks run support sometimes."
Cain, who entered the game with a Major League-low .166 opponents' batting average, surrendered seven hits to the first 13 hitters he confronted. He recovered by retiring 10 of the last 11 Cardinals he faced, including the final eight.
"That's one of those where you keep pushing yourself to go back out there and prove to the guys, 'I'm going to keep battling for you and hopefully you'll do the same for me,'" Cain said. "It kind of worked out that the guys did that."