Just 12 days ago, fellow rookie Derek Norris hit his first walk-off home run in a dramatic win over the Giants. This time, it was Carter's turn.
"It feels great," Carter said. "It's my first walk-off hit, first walk-off home run here in the Majors, and I haven't done it in a while. It's just awesome."
"I don't know if the ball's come down yet," quipped A's manager Bob Melvin. "Good swing.
"You know, in that type of situation, you've got to be ready, you've got to be up in the cage, you've got to be swinging, you've got to be hot, you've got to be ready and expecting to have your number called. He came down, everybody was ready when the inning started, and he put a good swing on it."
In winning its fifth straight game, Oakland got back to the .500 mark for the first time since the team was 22-22 on May 22. It was also the A's third straight one-run triumph, all of which have seen them score the winning run in the sixth inning or later. It also comes after another walk-off on Tuesday against the Red Sox.
Oakland's new-found resiliency and clutch late-game play, missing last year and earlier this season, has been a common topic for Melvin in recent days, as he's lauded the experience the A's have gained in such situations.
That experience paid off again on Friday.
"I think we're just going out every time and persevering," said second baseman Jemile Weeks, whose single in the eighth inning tied the game at 1-1. "Playing good defense, pitchers have been shutting teams down the best they can. We're just not giving in until the last out at the plate."
It looked for most of the game that the A's would go down to their Major League-worst 12th shutout at the hands of Seattle starter Kevin Millwood, with the A's getting more than one runner on base on just one occasion over Millwood's seven innings.
But in the eighth, Oakland finally produced a run, thanks to Brandon Hicks' pinch-hit double and Weeks' RBI single two batters later off Mariners closer Tom Wilhelmsen.
And in the 11th, Carter came through with the most important, and most powerful, hit of the night off Delabar.
"Coming in late like that, you've got to be perfect, and I wasn't perfect," Delabar said. "The location was up a little bit and he got it."
Lost in the late-game drama was the performance of left-hander Tommy Milone, as the rookie dazzled at home, per usual, in his final start before the All-Star break.
Over seven innings, Milone held Seattle to one run, which the Mariners tallied in the first inning. From that point on Milone was nearly untouchable, and he finished with a flourish by striking out the side in his final frame. That pushed his strikeout total to nine, a career high, and his ERA at the Coliseum now sits at 1.03.
"I tell myself when I go out there, I'm not trying to strike people out," Milone said. "I feel if I make good pitches, then strikeouts can come. I'm a guy that likes to get early contact and get the hitter out of there early, but it felt good tonight. I was throwing strikes to begin with and then leaving the zone when I had to."
Milone's performance continued a historic run. It was the seventh straight game in which the A's starter allowed one run or fewer, setting an Oakland record. Since 1921, the club's only longer streak was eight games in 1966, when the franchise was located in Kansas City.
Milone also avoided taking the loss, which was thanks to his teammates' scrappy play and the eventual heroics of another rookie.
Carter has struggled in his previous stints in the Majors, but looks like a different player now, having collected six hits -- three of them home runs -- in 12 at-bats since being recalled. Despite facing almost exclusively left-handers so far, his game-winner came against the right-handed Delabar.
Melvin credited the front office for bringing Carter up at a time when he was hitting well at Triple-A Sacramento, giving the 25-year-old confidence to start with.
That confident vibe seems to be shared by the whole team after the A's latest one-run win.
"It's always nice to get back to .500," Melvin said. "It's nice to be over .500, so that's kind of the goal now."