"Something I'll never forget," Norris said. "It's a great feeling."
With two outs and a full count on him, Norris' at-bat might've been the most dramatic moment in a weekend full of them during the second Bay Bridge Series this season. He battled with Casilla the whole plate appearance, taking a 3-1 pitch on the corner and foul-tipping the next offering, which Giants catcher Buster Posey couldn't hold on to.
Casilla then left a fastball over the plate, and Norris hit a no-doubter, becoming the first A's player to have his first home run be a walk-off since George Hendrick on May 28, 1972.
"I knew it was out as soon as he hit it," Giants manager Bruce Bochy said. "This one they got to walk off."
"Terrific at-bat," added A's manager Bob Melvin. "Just talk about grinding. Two strikes, the whole bit. Just a terrific at-bat."
For most of the game, it appeared that the affair was going to come down to a close call in the sixth inning. With the score 2-1 in favor of San Francisco at that point, and with runners on first and second and two outs, A's left fielder Seth Smith stepped to the plate with a chance to tie the game or take the lead against Giants starter Matt Cain.
It appeared Smith had gotten the hit to do so when he lined a 3-2 pitch to right field. But as Smith was rounding first, first-base umpire Todd Tichenor threw his hands up to signal a foul ball. That prompted Smith, too, to throw his hands up, in shock.
Replays showed that the ball might indeed have been fair, since chalk flew up when it hit the ground, but it was still inconclusive whether or not it actually hit the line.
Melvin came out to argue the call in vain, and Smith fouled out to left field a few pitches later to end the inning. In the team's only other real threat, right fielder Josh Reddick grounded to second for an inning-ending double play in the eighth, stranding shortstop Brandon Hicks at third.
But Oakland starter A.J. Griffin -- another rookie, and Norris' batterymate at Triple-A Sacramento until the catcher was called up Thursday -- was just as impressive as Cain in his Major League debut.
Called up Sunday to replace the injured Brandon McCarthy, Griffin had one key mistake, allowing a two-run homer to Posey in the first frame.
The rookie announced to the dugout after the inning that those were all the runs that San Francisco was going to get. He backed up his promise, pitching solidly the rest of the way.
"That was wishful thinking, and it just came to fruition," Griffin said. "I just wanted to go out there and give us a good chance to win."
Griffin retired 13 batters in a row at one point and allowed just those two runs over his six-plus innings, keeping the A's in the game long enough to set them up for their ninth-inning rally and Norris' heroics.
Though the game was almost marred by controversy thanks to Smith's foul ball, in the end, Sunday belonged to the pair of Oakland rookies.
Griffin said he was "speechless" while thinking about the events of the past two days, from landing in Las Vegas with the River Cats, to being told he was starting for the A's, to making his big league debut the next day in an important game in front of an impassioned crowd.
The starter admitted that he and Norris were both surprised to have reached the Majors so quickly. But if there were nerves on the part of either, it didn't show. Their day culminated in a critical win and a lasting memory for Norris, despite the near-blindness brought on by the shaving cream/water/Gatorade attack by his teammates after celebrating at home plate.
"It was a little surreal at first, but then once I got punched in the back of the ribs a couple times, it kind of kicked in, and then the pie in the face really set it in," Norris said. "It's a great feeling, and I'm glad we could get the 'W' today."