OAKLAND -- Jonathan Sanchez delivered a thorough performance Monday night, but it wasn't the kind the Giants would have preferred.

Sanchez displayed every facet of his pitching repertoire, from his assets to his flaws, in San Francisco's 5-1 Interleague loss to the Oakland A's. The assertive Sanchez blanked Oakland on one hit through three innings. His faltering alter ego surrendered four runs and five hits in the fourth and sixth innings, which was more than enough to doom the Giants on an evening when they mustered four hits.

Sanchez endured not only his fourth consecutive loss but also the second in a row that prompted manager Bruce Bochy to leave the left-hander's next scheduled start in doubt.

In one breath, Bochy called Sanchez's effort an "improvement." In his next, Bochy refused to commit to keeping Sanchez in the rotation.

"That's something we'll talk about tomorrow," Bochy said. "Right now there's something we're thinking about. We'll get together tomorrow about what we're going to do with Jonathan."

The Giants' scheduled off-day Thursday would allow them to push back Sanchez's next start to June 30 at St. Louis, the next day they'd need a fifth starter. Or they simply could demote Sanchez either to the bullpen or Triple-A Fresno, since he has a Minor League option remaining, and try somebody else. One possible alternative is right-hander Kevin Pucetas, who's 6-2 with a 3.59 ERA at Fresno. Ultra-prospects Madison Bumgarner (4-1, 2.13) and Tim Alderson (3-1, 1.82) are excelling at Double-A Connecticut, but the front office probably would prefer to let them mature a little longer.

Doing nothing and keeping the rotation intact in its current sequence is another possibility for the Giants. But given Sanchez's 2-8 record, 5.54 ERA and two quality starts in 13 tries, it's fair to question whether Bochy and general manager Brian Sabean will continue to remain patient with him.

Asked whether he believed he did enough to earn another start, Sanchez gave himself the nod. "I was working my butt off out there," he said.

He had to, because only one of the six innings he began proceeded in 1-2-3 fashion. He ultimately yielded four runs and eight hits while walking three in 5 1/3 innings.

"He competed well and had good stuff," Bochy maintained.

This was Sanchez: He aroused skepticism immediately by walking Adam Kennedy, the first batter he faced, on four pitches. He then retired the next three A's.

This, too, was Sanchez: After Travis Ishikawa gave San Francisco a 1-0 lead in the second inning with his third home run in five games, Jack Cust singled to open the fourth inning and stole second base -- his second career theft in 407 games. Even for Sanchez, who's known as an easy mark for basestealers, this was a little extreme.

Matt Holliday walked before Orlando Cabrera lined an RBI double. Sanchez toughened by retiring the next three hitters, though Ryan Sweeney's groundout scored Holliday.

Sanchez continued to demonstrate the competitiveness Bochy mentioned, escaping a second-and-third, one-out jam in the fifth inning by erasing Cust and Holliday on popups. Sanchez wasn't as fortunate in the sixth.

Cabrera again doubled before ex-Giant Rajai Davis hustled out a bunt single. Davis stole second, eliciting an argument from Bochy. But television replays indicated that umpire Eric Cooper called the play correctly.

"I thought we had him, but the guy who counts said we didn't, so it's automatic," said second baseman Matt Downs, who tagged Davis. "I looked at it on replay. It was a bang-bang play, but the umpires up here don't miss a lot. It probably changes the inning if we get him."

After Sweeney struck out, .191-hitting Bobby Crosby poked a 2-2 pitch through the vacant territory just inside first base for a double, scoring both runners.

That probably seemed like an avalanche of offense to the Giants. They couldn't solve rookie right-hander Trevor Cahill (5-5), against whom San Francisco went 0-for-5 with runners in scoring position.

"He kept his sinker down all night, and we chased it," said right-hander Nate Schierholtz, who went 0-for-3. "We really didn't give Sanchez much support."