SAN FRANCISCO — There is a fundamental flaw with the Giants’ offense — aside from their substandard on-base percentage, their lack of situational hitting and their almost complete power vacuum.

Bengie Molina, their catcher, is their best hitter. And that’s almost never a good idea.
The Giants were reminded of that inconvenient little notion in the sixth inning of their 7-4 loss to the New York Mets on Thursday night, when Molina writhed in the dirt after his right knee absorbed a painful foul tip.
Molina remained down for several minutes as trainer Mark Gruesbeck attended to him. The 34-year-old catcher gingerly squatted down and declared himself fit to continue as a crowd of 30,154 sighed.
Can you imagine if the Giants lost Molina because of a foul tip, home-plate collision or any of the other dangers that come with his territory? He leads the club with 29 RBI. Edgar Renteria is next, with 17.
And now Renteria might be a casualty. The shortstop will have an MRI exam on Friday after straining his right hamstring while beating out a game-tying infield single in the eighth inning. The Giants’ two-run rally couldn’t save them, as Brian Wilson allowed three more in the bottom of the ninth and the Giants lost their second consecutive game — something they had avoided since April 16, when they finished a winless six-game road trip to San Diego and Los Angeles.
As bad as the Giants’ offense has been, at least their position players had avoided significant injuries until now.
“The key to being successful is having your guys stay healthy,” center fielder Aaron Rowand said. “Thank God Bengie wasn’t hurt, and we’ll keep our fingers crossed with Edgar.”
Molina appeared OK while hitting a leadoff double in the ninth inning against Mets closer Francisco Rodriguez, his former World Series batterymate with the Angels.
“I was confident he would be fine,” Giants Manager Bruce Bochy said. “As a catcher, you know when it hits you where the shin guards are connected. It paralyzes you for a couple minutes, but it usually comes back.”
Renteria might need more time. If the Giants place him on the 15-day disabled list, Juan Uribe would become the everyday shortstop and infielder Kevin Frandsen would be the obvious choice to promote from Triple-A Fresno.
But the Giants could go in another direction, perhaps purchasing the contract of Jesus Guzman. The club is desperate for offense and Guzman’s bat is smoking at Fresno.
Carlos Beltran hurt the Giants and Wilson in the ninth. The Mets’ star centerfielder hit a one-out double and stole third base on a close play. Molina’s throw arrived ahead of Beltran’s slide, but replays appeared to show that third baseman Pablo Sandoval applied a high tag.
Bochy said it was hard to tell, but it appeared the Mets got a break. Wilson hinted his agreement.
“It’s a different mentality after that play,” Wilson said. “If he’s out, it’s a completely different inning.”
David Wright singled in Beltran with the tiebreaking run and Ramon Castro added a two-run single as the Mets brushed off their 12-inning loss from a day earlier.
The Giants’ rally in the eighth took Jonathan Sanchez off the hook for his third consecutive loss, but the team hasn’t won any of his last four starts. Sanchez allowed nine hits in 5·innings and failed to regain the focus that made him so tough to begin the season.
The Mets’ two-run rally in the third inning was typical. Sanchez had two outs and the bases empty before the Mets strung together three hits to score the tying and go-ahead runs.
While Bochy noted that Sanchez’s concentration was improved, he criticized the left-hander for failing to hold runners.
“Sanchy has got to get better at that,” Bochy said.
After Beltran’s key steal in the ninth, the same could be true for Wilson.