OAKLAND, Calif. — Matt Cain looked around the Giants clubhouse after Sunday's 4-2 walk-off loss to the A's and described the vibe as "tough" and "not a good feeling."

For Cain and the Giants, it was also a familiar one.

Cain, long notorious for his tough luck, was sharp through seven innings at the Oakland Coliseum but watched from the dugout as victory escaped the Giants at the last possible moment. Rookie Derek Norris hit a three-run homer on a two-out, 3-2 fastball from Santiago Casilla in the ninth, snapping Cain's eight-start winning streak.

With the first-place Los Angeles Dodgers coming into town for a three-game set, Cain and his teammates weren't in the mood to dwell on the tough loss or a 4-5 road trip.

"We've got to put this past us," Cain said. "That's part of being a professional—we've got to let things like this pass."

Cain, who remains 9-2, is as experienced at that as anybody in the big leagues. He has built his sterling reputation on his ability to handle brutal losses as seamlessly as big-time wins, and Sunday's was a tough one to swallow.

Buster Posey staked Cain to an early lead with a two-run homer in the first inning, his team-leading 10th of the year. But that lead was threatened on several occasions.

Cain ran into trouble in the sixth when he gave up a single and walk ahead of Seth Smith. A lengthy two-out clash ensued.

Smith was 2 for 25 lifetime against Cain but appeared to have a two-run double when he lined a shot down the right-field line. First-base umpire Todd Tichenor ruled the ball foul.

Replays appeared to show the ball kicking up some chalk, but that was no use to Smith. Cain got him to fly out on the 12th pitch of the at-bat.

"That was pretty intense," Cain said. "We've battled it out, and he's always given me a rough time. I was just worried about finding a way to get him out."

Jeremy Affeldt had the same concern in the eighth inning after the A's put runners on the corners with one out. But Affeldt got Josh Reddick to ground into an inning-ending double play, setting off raucous fist pumps across the infield.

Affeldt waited by the dugout to greet his teammates, but the positive vibes were short-lived.

Casilla allowed two singles, each followed by a strikeout, to set up Norris' decisive at-bat. Sergio Romo was warmed up and ready to go, but manager Bruce Bochy stuck with Casilla, who had been 20 for 21 in save opportunities.

"He was probably a little hyped up there at the end," Bochy said. "This guy has done such a terrific job, but occasionally you're going to have a hiccup."