SAN FRANCISCO -- The Trade Deadline is looming and the Giants are active in the market. San Francisco general manager Brian Sabean has declared his veterans and soon-to-be free agents readily available.

The club's young pitchers, though, are off-limits -- and for good reason. Albeit against an offensively challenged Nationals team, Matt Cain showed the locals why Sabean is intent on keeping his baby hurlers.

Toeing the mound with the flu and a five-walk outing in his immediate wake, Cain limited the Nationals to four hits and no walks with four strikeouts in a 1-0 victory on Thursday afternoon, capping both a three-game series and seven-game season sweep against Washington's finest.

Fans have adorned Tim Lincecum with the "franchise" tag, but Cain (6-8) showed that he's still the co-captain of the Giants' future. Sabean reiterated Sunday, the day he traded Ray Durham for two prospects, that he wouldn't deal Cain, Lincecum or Jonathan Sanchez. Cain gave that philosophy extra legitimacy with the way he closed out the Nationals.

After San Francisco scraped together the game's lone run in the eighth, Cain hit a snag in the ninth. He struck out Jesus Flores to get the first out, but allowed back-to-back hits to Willie Harris (single) and Cristian Guzman (double).

Manager Bruce Bochy trotted out to the mound to calm Cain -- see if he was OK to continue.

He was. Ryan Zimmerman popped up to right fielder Randy Winn, who rifled a throw home to keep Harris from tagging and scoring the tying run. Austin Kearns then hit a ball to the same place, Winn made the out and Cain finished his first shutout of the season, the second of his career. The 23-year-old righty didn't walk a batter for the first time since Sept. 16 -- he'd walked 14 in his past four starts alone.

"He had some easy innings and I pretty much made up my mind that it was his day," Bochy said.

Cain knew one swing of the bat by Zimmerman could have ruined his afternoon, and he relished the challenge of retiring him.

"I almost wanted him to beat me," Cain said of his decision to attack the strike zone against the slugger instead of walking him to load the bases and set up a force play at every station. "It would make me feel better to really go at him, to really just challenge him to try to see what he could do."

For the first eight innings, neither team's batters did much of anything. Nationals starter Tim Redding (7-5) threw his first complete game, scattering seven hits with no walks over eight innings.

Aaron Rowand, Steve Holm and Dave Roberts were the only sources of Giants offense, each stroking two singles. Rowand isn't on the trade market; he signed with the club for five years in the offseason. Holm, called up Wednesday from Triple-A Fresno, wouldn't draw much attention even if he were on the block.

Roberts, though, a veteran with a terrific clubhouse presence, could be in the midst of a one-week trade audition. In his first start since landing on the disabled list in early April with a knee injury, Roberts made a leaping catch in the sixth inning and stroked the tiebreaking RBI single in the eighth that scored Eugenio Velez from second base. Velez, running for Holm, had reached second on Cain's bunt.

Showing no rust from his brief rehab stint in the Minors, Roberts singled in his first at-bat despite admittedly not getting many Zs the previous night.

"I was tossing, turning, waiting for the alarm to go off," Roberts said. "I lost a lot of sleep last night looking forward to playing today. Just having the support of my teammates, they were so excited to see me back in the lineup ... it means a lot."

What Roberts did in the game meant a lot to Cain, too.

Working with a slower-than-usual fastball in the low 90s, Cain said he was hitting his spots better than usual. He was forced to focus more on his pitch location because he couldn't rely on his overpowering stuff, which he was without because of his sickness.

Cain's best 2008 performance gives the Giants some much needed momentum heading into a stretch beginning Friday in which they play 12 of 15 games against National League West opponents. Currently in fourth place in the division, seven games out of the lead, San Francisco equaled its longest home winning streak (three games) since April 8-10.

The Giants (43-58) are 20-31 at home, worst in the NL, but they hope the upcoming series against Arizona will end their recent woes at AT&T Park.

If they could play the Nationals more often, they'd probably make a run for the pennant. San Francisco swept the Nationals this season (7-0) and has won 11 of its past 15 games against the club.

If they get more efforts like Cain's from all of their young pitchers, they could make Sabean's recent pitcher-hoarding mind-set look genius.

"It is an invaluable experience for him pitching in the ninth and learning how to close the game," Bochy said. "That is something he can build on. He is a horse out there.

"These guys pitch the way Matt did today," Bochy said of his coveted young pitchers, "we are going to let them go."