DENVER -- Monday's holiday notwithstanding, school was definitely in session for Matt Cain.

A month shy of turning 23, Cain's younger than any of the Giants' rookies, despite possessing more than two years of Major League service time. The right-hander's still learning, and his Labor Day lesson was one that will require resilience after the Giants lost their third consecutive game, a 7-4 setback against the Colorado Rockies.

Cain found how elusive a pitcher's best stuff can be. After striking out five of the first eight hitters he faced, he unraveled in the third inning as Colorado scored seven runs, all but one of which were charged to him.

"That's what's frustrating. You want to run with that," said Cain, whose 2 2/3-inning outing was the briefest of his career.

Afterward, Cain (7-14) searched for answers like an English major in physics class.

"It's almost as if I didn't really know what happened," he said. "I was making good pitches. They were taking pitches that were close, they worked counts and then they put the ball in play."

Cain's confusion was prompted by an unlikely opponent. He has faced the Rockies 11 times, more than any other opponent. He was well aware of their offensive prowess, which made them the National League's second-highest scoring team entering Monday. Yet he also knew how to tame the Rockies, as his performance against them indicated. He was 5-2 with a 2.40 ERA lifetime against them entering the game, including 2-0, 1.35 this season. In four previous appearances at Coors Field, a hitter's paradise, Cain took a respectable 3.33 ERA into Monday's start.

Lately, Cain has looked good against everybody. He finished 4-1 with a 2.18 ERA in August, reversing his season-long streak of ill luck by winning his last three starts.

All that unraveled in the Rockies' big third. Opposing pitcher Jeff Francis, who entered the game with a respectable .173 batting average, ignited the rally with one out by doubling to right-center field after fouling off four 2-2 pitches. Willy Taveras' single put runners on the corners before Kaz Matsui lined an RBI single and Matt Holliday lifted a sacrifice fly. Cain issued two-out walks to Todd Helton and Garrett Atkins, loading the bases and prolonging the inning for Brad Hawpe's two-run single to right. Out went Cain, who threw 44 pitches in the third inning after uncorking 25 in the first two. In came Patrick Misch, who surrendered Troy Tulowitzki's RBI single and Chris Iannetta's two-run triple into the right-field corner.

"We're not going to take any chances," Bochy said, explaining Cain's removal. "It was getting to a point where you're risking injury with a guy, throwing that many pitches."

Cain couldn't quite accuse himself of being shelled. Rookie Nate Schierholtz, starting his first game in right field at Coors Field, dove for Francis' double after a long run and barely missed catching it. Schierholtz also seemed to break uncertainly for both Matsui's and Iannetta's hits. At least one Giant believed plate umpire Bruce Dreckman "squeezed" Cain by robbing him of called strikes, particularly an 0-2 curveball to Matsui. But neither could Cain point to bad luck, given the way he allowed the inning to mushroom.

"Either way, this is not a fun loss," Cain said. "I'm trying to look past this start, build off what I did the first two innings and the rest of the season and try to put this past me and not let it ruin this month."

Following Cain's example, Schierholtz took his outfield adjustment in stride, given his strange surroundings. This also was the first day game he had played in close to a month, by his estimation.

"It takes time sometimes," said Schierholtz, who went 2-for-3 in his first start since being recalled last Saturday. "You like to do as much early work as you can in batting practice. After a series or so, it's a little bit different."

The Giants tried to redeem the afternoon by whittling their 7-1 deficit and even sent Barry Bonds to the on-deck circle as a pinch-hitter and the potential tying run in the eighth inning with Schierholtz on first, two outs and Kevin Frandsen batting. Frandsen lined out, but he already had contributed in his previous at-bat by lining a sixth-inning RBI single off Francis (15-6) to end a 12-pitch confrontation. It was a September moment, featuring a young player striving to excel.

"I went up there with a 'This-guy's-not-going-to-beat-me' attitude -- just like every other at-bat, but I made sure," Frandsen said.