How did the San Francisco Giants suddenly become so vulnerable?

What’s up with the San Francisco Giants?

Lost in the euphoria of Clayton Kershaw’s no-hitter Wednesday was the fact that the 8-0 victory brought the Dodgers to within four games of the Giants in the National League West.

On June 8, the Dodgers were 9½ games back. Since then they’ve gone 8-3, which is a nice little run, but not the kind that typically makes up 5½ games in 11 days.

The Giants are giving the Dodgers inspiration with their suddenly lousy play. The Halloween-colored kids have lost five consecutive games and eight of their last nine.

They’re practically begging the Dodgers to get back into the race.

What gives? How did the team with baseball’s best record, that was 21 games over .500 and giving no indication it would fall back to the pack, go into such an unexpected tailspin?

Best to begin with their starting pitching, which during their nine-game skid has a fat 5.63 ERA. This is a rotation that features what’s left of Tim Lincecum (5-4, 4.81 ERA, 1.40 WHIP) and Ryan Vogelsong (4-3, 3.94, 1.34). Matt Cain (1-5, 4.52, 1.26) has already made two trips to the disabled list. And they continue to count on 38-year-old Tim Hudson to drink from the Fountain of Youth (his current 2.39 ERA would be a career-low).

Then Brandon Belt remains on the DL with a broken thumb, second baseman Brandon Hicks has stopped hitting and Angel Pagan is dealing with a back issue.

Meet the unexpectedly vulnerable Giants.

Apparently the Giants are going to have to turn things around with the horses they already have.

“It’s a long time from thinking the cavalry’s going to come,” Giants General Manager Brian Sabean told the San Francisco Chronicle’s John Shea. “You’re not going to execute a trade at this time of year.”

Sabean has been through all these wars before and prefers to take the long view, figuring — hoping — it’s just one those slumps every teams goes through during the course of a 162-game season.

“You have to keep it in perspective,” he said. “We were all surprised we ran to 21 games over .500. Having said that, we’re surprised we’ve lost eight of nine.”

Meanwhile, buoyed by Kershaw’s no-hitter and the Giants’ swoon, the Dodgers have some unexpected giddy-up in their step.

This is the closest the Dodgers have been to the Giants in a month. And Friday night in San Diego they can post their fourth victory a row, which would be their longest winning streak of the season. Imagine what could happen if they actually ever get hot.