SAN FRANCISCO -- Nothing was ordinary about the Giants' series opener on Friday night against the Diamondbacks -- except the result, which was a 4-3, 10-inning loss for San Francisco.

Barry Bonds hit his 750th home run, which made this game singular enough. He also received a seventh-inning visit from a spectator who somehow skirted ballpark security and strode to him in left field. Fortunately for Bonds, the fan proved harmless.

Center fielder Dave Roberts dropped an easy fly ball in that same inning, generating two unearned runs for the D-backs that erased San Francisco's 2-1 lead. Although the Giants pulled even one inning later on Bonds' homer, Roberts' misplay spoiled an otherwise stellar defensive effort.

The Giants' third consecutive defeat was sealed when Arizona's Miguel Montero homered off Brad Hennessey (1-3) with one out in the 10th, breaking a 3-3 deadlock. Nine of this season's 10 games between Arizona and San Francisco have been decided by one run. The other was a two-run margin.

Giants manager Bruce Bochy sounded as if his patience with his last-place club had almost expired.

"This is getting borderline ridiculous, how these games are going," Bochy said. "Right now we're all embarrassed where we're at, how we're playing."

Nobody was more embarrassed than Roberts, who committed his misplay with Orlando Hudson on second base, Stephen Drew on third and two outs in the seventh. Conor Jackson lifted a harmless-looking fly ball that appeared destined to end the inning. The ball drifted slightly to right-center, but Roberts still appeared to have a play on it until it squirted out of his glove, enabling Hudson and Drew to score.

Asked what happened, Roberts said, "I have no idea. It's a routine play. It's a play I've made a thousand times. There's no excuse for it. We've got 24 guys doing their job to turn this thing around, and I drop a routine fly ball to cost us the game. It's ridiculous."

Giants starter Matt Morris, who lasted seven innings, spoke forgivingly of Roberts.

"I'll take Dave out there every time," Morris said. "He battles his butt off at the plate, he battles in the field. Things just aren't going well for us. Things like that tend to happen to teams that are down. ... Dave's one of the main guys on this team who keeps us together and playing hard. It's just unfortunate."

The Giants' fortunes briefly improved as Bonds led off the eighth against ex-teammate Livan Hernandez with his 16th home run of the season, tying the score and leaving him five homers short of Hank Aaron's all-time record of 755. It also set up the Giants' fourth extra-inning affair in six games.

But Montero's homer off Hennessey exposed another flaw. Giants pitchers surrendered three homers to San Diego in Tuesday's 3-2 setback that christened the losing streak.

"That long ball's killing us, too," Bochy said. "We've had a lot of them late in the ballgame. It's been the difference in these one-run games for us. But we also have to make plays in these tight ballgames, and tonight we didn't."

In fact, the Giants' tendency to play low-scoring, close games leaves no margin for error. They're 11-15 in one-run games, 6-14 in two-run decisions. "We need that extra hit or extra run to give us some leeway or put us on top, and we're not getting it," Morris said. "There's a lot of pressure on the pitchers late in the game. We're making mistakes and it's costing us."

The Giants' collapse offset Ryan Klesko's sixth-inning homer, which broke a 1-1 tie. It was the 44th "Splash Hit" into McCovey Cove, the portion of San Francisco Bay beyond the right-field wall, since AT&T Park opened in 2000.

San Francisco's loss also negated the wizardry of shortstop Omar Vizquel, who did not figure in the scoring but had plenty to do with suppressing Arizona's offense. Vizquel, who missed San Francisco's previous two games with a strained right groin, asserted his presence by recording four slick assists, including a subtle fourth-inning play that helped save a run. With D-backs on the corners and one out, Vizquel corralled Carlos Quentin's grounder up the middle and shoveled the ball from his glove to second baseman Ray Durham, who barehanded the relay, stepped on the bag and fired to first for the double play.

The evening could have been much worse for the Giants if the fan who ambled toward Bonds had malevolent intentions. But Bonds actually chatted with him, draped his arm around him and led him toward security personnel who hustled him from the ballpark.

San Francisco Police identified the man as Andrew B. Clapp, 24, of Fargo, N.D., and charged him with trespassing on the field during play and public intoxication, both misdemeanors.

"My first feeling was fear," Roberts said. "I kind of made my way toward Barry and saw how [Clapp] was making his way toward Barry. He just wanted to shake his hand. Barry handled it like a pro, and I'm glad that the situation was defused, but that's something that can't happen."

Kind of like a dropped fly ball or an opponent's extra-inning home run.