Pence provided an example Monday night, hitting a three-run drive deep into the left-center seats in the first inning, and Posey added a late RBI single as the San Francisco Giants snapped the Colorado Rockies' five-game winning streak with a 4-2 victory.
"He's got some of the most power I've ever seen," Posey said. "I get to hit with him in BP every day, and I try to make sure I hit before him so I don't have to follow up his moonshots."
Madison Bumgarner (2-0) won his sixth in a row against the Rockies and owns a seven-start unbeaten run in the rivalry. The left-hander began his career 0-3 against Colorado in five starts.
He struck out five and walked five in 5 2/3 innings Monday, allowing two runs and five hits.
One of those was Carlos Gonzalez's long homer to right in the third. The ball bounced off the pathway and splashed into McCovey Cove.
"He was throwing a lot of good pitches," Gonzalez said. "I think that was the one mistake he threw and I hit it out."
San Francisco extended its winning streak against the Rockies to seven games and bounced back from a 14-3 loss to St. Louis a day earlier when ace Matt Cain was tagged for nine runs in the fourth inning.
Michael Cuddyer had two hits and stole his first base for a Rockies team that had won five in a row since losing its opener 5-4 in 10 innings at Milwaukee. Dexter Fowler had his six-game hitting streak to start the season snapped as he went 0 for 4 with two strikeouts.
Pence sent the first pitch he saw from Jorge De La Rosa (0-1) deep into the bleachers in left-center for one of the hardest, longest balls he has hit at home since joining the Giants last July. Pablo Sandoval singled twice and scored a run.
The reigning World Series champions returned to a more normal routine after three straight days of celebrations -- the flag raising Friday for the home opener, Posey's NL MVP presentation Saturday and then Sunday's ring ceremony.
Bumgarner pitched a 1-2-3 first, then issued at least one walk in each of the next four innings. After Cuddyer drew a leadoff walk in the fourth, Bumgarner was helped by a double play to get out of it unscathed. He walked Yorvit Torrealba to start the fifth, then Eric Young Jr. one out later before Bumgarner escaped another jam.
He is off to a solid start after struggling last postseason. Bumgarner, who spent the winter working on his mechanics, is trying to build on a 2012 season in which he won a career-best 16 games and had a 2.33 ERA in 14 home outings.
"I didn't feel like I had trust in my stuff the way I did last time," he said. "I had a few mental lapses."
The curveball to Gonzalez was one of those he didn't have the "conviction" behind, as he put it.
"It would be hard to hit it any better," Bumgarner said.
Casilla went 1 1/3 perfect innings, Jeremy Affeldt pitched a clean eighth and Sergio Romo allowed Josh Rutledge's leadoff double before striking out the side for his fourth save as the Giants retired 10 of the final 11 Rockies batters.
Posey's two-out single in the eighth provided some insurance.
De La Rosa allowed six hits and his only runs on Pence's homer, struck out three and walked one in a 76-pitch outing over six innings. He is 0-4 in his last seven starts dating to 2012.
Colorado starters reached 109 straight games without throwing 100 pitches, the longest such streak since pitch count data began in 1988.
The Giants went 14-4 against the Rockies last season for their most wins in the series, including 7-2 at AT&T Park.
First-year Rockies manager Walt Weiss returned to the Bay Area, where his big league career began as a first-round draft pick by Oakland in 1985. He spent the initial six of his 14 major league seasons with the Athletics.
"Welcome back, Walt!" one fan hollered as the skipper emerged for batting practice. He smiled and waved.
"We had Bumgarner on the ropes a couple of times after he walked a couple of guys but he pitched his way out of some jams," Weiss said.
Fowler is batting .323 (10 for 31) with four homers, five RBIs and seven runs. ... Bumgarner is 6-3 vs. Colorado in 12 career outings and went 3-0 against the Rockies in 2012. His 2.45 ERA is second-lowest vs. the Rockies of any active pitcher (behind St. Louis' Chris Carpenter, 1.41). ... Rockies 1B Todd Helton had a second straight day off before pinch-hitting in the ninth. Weiss plans to start him Tuesday night. Helton had surgery last August to repair a torn labrum in his right hip. ... Colorado hasn't won a series in San Francisco since taking two of three from May 31 to June 2, 2010. ... RHP Tim Lincecum (1-0) pitches Tuesday night for the Giants against RHP Juan Nicasio (1-0).