Torrealba's bases-loaded hit into the left-center field gap allowed the Rockies to pull out a comeback win and remain two games behind the first-place Los Angeles Dodgers in the NL West. Los Angeles beat the Giants 10-3 at San Francisco.
"We've had some dramatic games since the end of May, but that one there goes to the top of the list," Rockies manager Jim Tracy said.
Colorado, with a major-league best record of 62-28 since June 4, had been held to just three hits off five Padres pitchers before tagging Bell with his first blown save at home. The NL co-leader with 37 saves gave up four runs on three hits and two walks.
Torrealba, who came into the game defensively in the seventh inning, fell behind 0-2 before he connected on Bell's 2-2 fastball.
"He surprised me that he threw so many fastballs," Torrealba said. "At 2-2, I figured he would throw me a fastball since he doesn't want to go 3-2. It seems like he doesn't feel comfortable throwing his slider."
Bell (5-3), who has four blown saves, struggled with his control throughout the inning.
"My mechanics were off and I wasn't hitting my spots," he said. "I should have thrown him a curve ball. If I had thrown him a curve ball, I think we would have won the game. He's not a good breaking ball hitter. I should have thrown a breaking ball. It's probably a better percentage pitch."
San Diego was on the verge of handing the Rockies a tough loss in their playoff chase with 20 games left in the season after Jorge De La Rosa walked in the game's only run in the first inning.
But Colorado rebounded for its eighth straight win as the Rockies increased their lead in the wild-card race to 5½ games over the Giants. Colorado raised its record to 10-1 in September, tops in the majors.
"After being down 1-0 almost all game, to be able to come through off the bench, it was huge," Torrealba said. "We're trying to get to the playoffs, so it's pretty exciting."
Torrealba is 13 for 18 (.722) with runners in scoring position since May 29.
"That's just an unbelievable game," Tracy said.
De La Rosa allowed one run on five hits in seven innings. He walked four and struck out eight to set the club single-season record for strikeouts by a left-hander with 170.
Edward Mujica made his first career start and allowed two hits in four scoreless innings.
San Diego loaded the bases in the first inning on David Eckstein's one-out double, a walk to Adrian Gonzalez and Chase Headley's bloop single that hit off the glove of second baseman Clint Barmes in short right field. Barmes had the ball in his glove before it popped out as he hit into a sliding Hawpe.
De La Rosa then walked Salazar on four consecutive pitches to force in a run. De La Rosa got out of the inning by getting Will Venable to ground into a double play.
Mujica's first major league start came after 116 career appearances out of the bullpen. The right-hander drew the start in place of rookie Mat Latos, who has been shut down for the season due to the number of innings he's thrown.
- Rockies RHP Jose Contreras, who left Thursday's 5-1 win over Cincinnati with right quadriceps strain, will probably not make his next start, Tracy said.
- De La Rosa broke the Rockies' single-season strikeout mark by lefties set by Jeff Francis in 2007.
- The Padres will honor the Park View All-Stars, who recently won the Little League World Series, before Saturday's game against the Rockies. Park View, from nearby Chula Vista, will take batting practice with San Diego's last group.