With Yomiuri holding the tiebreaker, Wednesday's win over the Hanshin Tigers was likely the backbreaker.
The Giants, who trailed in the Central League standings by as many as 13 games behind Hanshin on July 9, got an early two-run double from Lee Seung Yeop and a late home run from Alex Ramirez to take down the Tigers 3-1.
Yomiuri won the season series 14-10--taking the head-to-head tiebreaker should the teams finished with identical records--and now has a one-game lead in the standings with three games left on the schedule for both teams.
The Giants have a magic number of two to seal a second straight league title.
"We're excited. We're now a step ahead of them, but there is more work yet to do," said Yomiuri skipper Tatsunori Hara.
"We still have some important games left to play."
Ramirez, whose 43rd blast came in the seventh inning and gave him the CL lead, said the Giants felt confident going into the game.
"Today was the biggest game of the year for us and we prepared ourselves pretty good and we showed it today."
Yomiuri starter Testuya Utsumi (12-8), before a record crowd of 46,783 at Tokyo Dome, worked 5-2/3 innings, pitching around four hits and six walks with a pair of strikeouts to earn the win. The lefty improved to 4-1against the Tigers, winning his third straight decision against them in a runner-filled 91-pitch outing.
But reliever Tetsuya Yamaguchi played an even bigger role in the win, cleaning up Utsumi's mess in the sixth and finishing with two innings of scoreless relief to keep Hanshin in scramble mode.
"Yamaguchi came on and did a great job of shutting them down and keeping the game where it was," Hara said.
Kiyoshi Toyoda got the lone batter he faced in the eighth, and Marc Kroon got his 40th save with a perfect ninth.
"We had our chances to get even, but we weren't able to do it," said Hanshin manager Akinobu Okada, who added that the race is not over until it's over.
"This will probably go down to the wire."
The Giants took the lead in the third inning off loser Yuya Ando (13-9), thanks to four straight batters reaching base.
Ryota Wakiya opened the frame with an opposite-field single to left and Michihiro Ogasawara walked. Makoto Imaoka dove to knock down Ramirez's hard grounder to third and keep it on the infield for a single before Lee split the gap in left center for a double and a 2-0 Giants lead.
"I wanted make sure I got the ball up in the air," Lee said. "I knew I couldn't hit into a double play or strike out in that situation, so I concentrated on trying to get the runner home from third, since there was only one out."
Ando--who fell to 1-4 against the Giants this season--fanned Yoshiyuki Kamei for the second out and, after an intentional pass to Shinnosuke Abe, got Hayato Sakamoto to fly out and end the inning.
The Tigers shot themselves in the foot in the first two innings. With Norihiro Akahoshi--who had three hits--on first and no outs, Abe pounced on Kentaro Sekimoto's sacrifice bunt attempt and fired to second to start a rally-ending twin-killing.
In the second inning, Takashi Toritani's double play ended the inning after Imaoka had walked with one out.
The Tigers got to Utsumi for a run in the sixth inning. The Giants lefty walked three in the frame, including Akihiro Yano, who worked the count full and took the ninth pitch for a free pass and an RBI.
Yamaguchi replaced Utsumi and got pinch-hitter Shinjiro Hiyama on a broken-bat grounder to second to end the inning.
Yamaguchi put the tying runner on second in the seventh, but got Takahiro Arai on a flyout to right to escape that threat.
Ramirez then blasted a towering solo shot to center, to make it 3-1.
The Giants play their home finale tonight against the Yokohama BayStars, and then play the next two nights against Tokyo Yakult at Jingu Stadium.
The Tigers play two at Yokohama starting on Friday before wrapping up their season on Sunday at Kobe's Skymark Stadium against the Dragons. The Tigers will also play all their postseason games in Kobe.