SAN FRANCISCO -- Although the composition of the Giants' Opening Day lineup remains an intriguing unknown, it quite possibly won't be the contingent manager Bruce Bochy calls upon the most in 2008.

Bochy used 124 different lineups in 2007, and he indicated before Thursday's 7-2 exhibition loss to the Seattle Mariners at AT&T Park that this kind of variety could emerge again as he searches for suitable combinations among the Giants' mix of veterans and relatively untested youngsters.

Bochy might have to experiment actively early in the season, depending on the physical condition of various Giants. Left fielder Dave Roberts, a possible regular, missed his third consecutive game Thursday with a sore left knee. Second baseman Ray Durham played his second exhibition in a row, but his injury history suggests that his tight left hamstring could nag him at any time. Even after shortstop Omar Vizquel returns from left knee surgery, which could be as soon as mid-April, Bochy probably will have to rest him periodically to keep him fit.

While Bochy would prefer to employ a set lineup -- what manager wouldn't? -- the Giants' tenuous health and instability at the infield corners might force him to mix and match constantly.

Citing factors that could influence his selections, Bochy said, "It may be a matchup. We may give up defense to try to get some runs. [Or] we may go with our defense."

Bochy prefers the term "matchup" to "platoon." Yet it's a near-lock that Roberts, who batted .156 against left-handers last season and owns a .238 career average against them, will sit against left-handed starters while Rajai Davis plays.

Other choices might not be so obvious, aside from when a particular hitter-versus-pitcher confrontation favors the Giants. Bochy can employ a lineup featuring as many as four switch-hitters -- Vizquel, Durham, Randy Winn and Dan Ortmeier -- which minimizes the need for platooning.

Yet Ortmeier, despite last year's statistics (.310 against right-handers, .257 against lefties), is more comfortable from the right side, which is his natural stroke.

"Left-handed has been somewhat of a mystery. Right-handed, he's a threat," Giants general manager Brian Sabean said. Since Rich Aurilia, the other prospective starting first baseman, also bats right-handed, Bochy still might elect to use Ortmeier against certain right-handers.

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A lineup that emphasizes offense likely would include both Durham and the dynamic Eugenio Velez, who's hitting .303 with a Major League-high 14 stolen bases and 13 RBIs, tied with Aurilia for the team lead. Since Velez appears to be most comfortable at second base, he'd have to play third or perhaps the outfield, where he has spent one inning all spring after playing 66 games there in the Minors last year, if Durham were starting.

Thursday, Durham drove in a run with a seventh-inning single, one of only five hits the Giants collected.

Based on current trends, an offense-oriented group also could feature outfielder Fred Lewis, who's batting .279, tallied a Cactus League-high four triples and ranks third on the Giants with 12 RBIs. Lewis went 0-for-3 Thursday but drew two walks, hiking his team-leading total to 11. Roberts, the 35-year-old leadoff man who hit .296 in last season's final three months and is hitting .283 this spring, has performed respectably. But it's clear that Lewis is poised to receive more than just sporadic activity.

"I know what I'm capable of doing," said the quiet yet determined Lewis, 27.

"Freddy's an exciting player," Bochy acknowledged. "There's no reason he couldn't be one of the better outfielders in the National League."

But Lewis, who occasionally takes uncertain routes toward fly balls, might be left out if Bochy wanted to emphasize defense. That, said Bochy, "is an area he can improve on and needs to improve on." The Roberts-Aaron Rowand-Winn trio, featuring three players capable of playing center field, is the outfield Bochy probably would favor if he wanted to suppress opposing offenses.

Jose Castillo, acquired last Saturday on waivers from the Florida Marlins, might find himself in Bochy's favorite defensive infield, most likely at third base.

"You can tell he's a good defender. He's going to help us out there," Bochy said of Castillo, Pittsburgh's regular second baseman from 2004-06.