Not even the team with the second-best record in the AL could stop them from taking an 8½-game lead in the AL East.
Boston's record is the best in both leagues -- 26-11 after Monday night's 7-1 win over the Detroit Tigers.
"I didn't see any reason to take him out," Red Sox manager Terry Francona said after Matsuzaka's first complete game since he had 13 in Japan last season. "He was better at the end than he was at the beginning."
Matsuzaka (5-2) got 16 outs on grounders and five on strikeouts. He allowed no walks for the first time in his eight starts. After three mediocre outings in which he allowed 17 runs, the right-hander with a multitude of pitches has given up just two runs in his last two games covering 16 innings.
"I thought he was better tonight than he was the last time," when he gave up one run in seven innings against Toronto, Francona said.
On Monday, Matsuzaka gave up six hits and was outstanding after Curtis Granderson's solo homer, his seventh, in the third. No other runners made it past second base.
"I wouldn't say that my stuff was the best that I've ever had" in the majors, he said through a translator, "but as for the results, I'm definitely the most happy about what happened today.
"But, at the same time, I don't want to settle and have to say that, going forward, the way I was pitching today was the best I can pitch."
Matsuzaka got the Red Sox off to a great start in the four-game series between the AL's two top teams.
"I was very impressed," Detroit manager Jim Leyland said of the rookie the Red Sox invested $103 million in. "He's the real deal."
The AL Central-leading Tigers fell to 23-14 with their second straight loss. Both teams are 11-3 in their last 14 games.
Boston's 8½-game division lead is its biggest since it held the same margin after play on Sept. 26, 1995. The idle New York Yankees dropped 8½ games back, their largest division deficit since they trailed by nine games after play on May 7, 2005.
"We have to continue to play good solid baseball and it has to start with our pitching," catcher Jason Varitek said. "We can't scoreboard watch."
The Red Sox, now 20-0 when scoring at least five runs, tied it on David Ortiz's RBI single in the third off Nate Robertson (3-3). Coco Crisp singled home the go-ahead run in the fourth and Manny Ramirez added a run-scoring single in the fifth.
The Red Sox kept fouling off pitches in the fifth. Robertson left after the inning, having thrown a season-high 115 pitches even though he didn't walk anyone.
"They do grind out a lot of at-bats," he said. "Pitchers throw a lot of pitches against them. I threw three good pitches for strikes tonight. They fouled off some good pitches."
Matsuzaka became the fourth five-game winner in the AL, joining teammate Josh Beckett, with seven wins, and John Lackey of the Los Angeles Angels and C.C. Sabathia of Cleveland, with five each.
"His fastball was in the mid 90s," Granderson said. "Once he established that, he threw his cutter, curve and changeup."
Matsuzaka threw a season-high 124 pitches in Boston's first complete game of the season after taking the mound in the ninth to a loud ovation.
"He reared back in that ninth and had a little adrenaline rush from the fans," Varitek said.
- Ramirez's RBI gave him 1,540 for his career and moved him into a tie with Willie Stargell for 38th place on the career list. He had been tied with Harry Heilmann. Next on the list is Fred McGriff with 1,550.
- J.D. Drew was the only Red Sox starter who did not get a hit.
- Detroit and Boston entered the game with the AL's two best batting averages in May, but Detroit's ERA for the month was 27th in the majors while Boston's was fifth.
- The Tigers lost for the second time in their last eight road games.