Giambi saved the Yankees on Thursday, coming off the bench to hit a tying homer in the seventh inning and a game-winning single in the ninth for a 3-2 victory over the Boston Red Sox.
Desperate to get back in the pennant race, New York salvaged the finale of a three-game series and won Boston's final regular-season game at Yankee Stadium.
"We have a pulse," Giambi said. "Hopefully, this will jump-start this ballclub."
Finally showing some spunk, New York moved within six games of the Red Sox, who lead the AL wild-card race. A series sweep by Boston would have left the Yankees eight games back with 29 to play - perhaps too steep a hill to climb.
The Yankees haven't missed a postseason since 1993, though their chances this year still look bleak.
"I don't care about the first two games - this one hurt," Red Sox manager Terry Francona said. "We played our hearts out. We lost a really tough game."
Boston also got bad news about ace Josh Beckett, who plans to have his ailing right elbow examined Friday by Dr. James Andrews in Alabama. Beckett was scratched from his scheduled start Friday night against the Chicago White Sox and will be replaced by Daisuke Matsuzaka.
Mariano Rivera (5-5) entered a tie game in the eighth and pitched 1 1-3 hitless innings for the win, helping the Yankees overcome another poor performance by Alex Rodriguez.
Booed vociferously all afternoon, A-Rod struck out three times and popped up with runners at the corners and one out in the sixth.
The three-time MVP also had a terrible game Tuesday night, going 0-for-5 and grounding into a pair of double plays during a 7-3 loss.
This time, Giambi brought the Yankees back.
"That was a huge win for us," Rodriguez said. "A loss there would have been very crucial."
Rested against lefty Jon Lester, Giambi pinch hit with two outs in the seventh and connected for a two-run homer off Hideki Okajima that tied the score 2-all.
With the bases loaded and one out in the ninth, Giambi lined Jonathan Papelbon's 0-2 pitch into center field and was mobbed at first base by elated - and relieved - teammates.
"It was a great way to end it," Johnny Damon said.
After two comfortable wins by the Red Sox the previous two nights, the teams played the kind of tense, back-and-forth game that has marked their long rivalry.
The Red Sox fell to 285-484-4 at Yankee Stadium. New York will move next year into a $1.3 billion ballpark being built across the street.
"It's sad to see it go, but I think it'll be fun to move to the new stadium," Lester said. "I'm sure everything will be fantastic."
Babe Ruth and the Yankees opened the current stadium by sweeping a four-game series from Boston in April 1923. Eighty-five years later, the Red Sox tried to return the favor.
Looking for its first sweep in the Bronx since April 2004, Boston got a fine effort from Lester but couldn't solve old-pro Mike Mussina or New York's bullpen.
"You don't ever want to get swept, especially in the situation we're in," Mussina said. "We had to really fight to win that last one."
Xavier Nady opened the ninth with a single off Justin Masterson (4-4). With one out, pinch-runner Brett Gardner stole second and Hideki Matsui was intentionally walked.
Masterson walked Ivan Rodriguez, loading the bases and bringing on Papelbon.
Lester was working on a four-hit shutout when Cody Ransom doubled with two outs in the seventh, chasing the lefty after 119 pitches.
Giambi's foul popup on Okajima's first pitch faded just enough to land on top of the dugout, and the slugger drove the next delivery off the front facing of the black batter's eye in center for his third career pinch-hit homer and second this season.
Lester sat stone-faced in the Boston dugout as Giambi circled the bases and the crowd roared. He came out for a curtain call, now 3-for-8 with two homers against Okajima.
"We've been stale. We haven't been able to get the big hit. We haven't been able to make a big pitch," Giambi said. "Hopefully, this turns it around."
Looking for his 267th win and 17th this season, Mussina gave the Yankees the strong start they lacked in the first two games. He allowed two runs and five hits in seven innings.
With his 2,774th career strikeout, the 39-year-old right-hander passed Frank Tanana for 20th place.
Lester was even better, shutting down New York for the third time this season. He struck out eight and walked none.
Mussina, a six-time Gold Glove winner, saved a run with an astoundingly quick stab of Jacoby Ellsbury's liner to end the seventh.
Notes: After fouling out in the sixth, A-Rod banged his bat against the rack nearly 10 times before taking a seat. ... RF Mark Kotsay doubled in his first plate appearance with Boston.
