Matsuzaka (7-2) had to wait out a pregame rain delay of one hour and 57 minutes before he could pursue the win that tied him for the Major League lead with teammate Josh Beckett (7-0), the Braves' John Smoltz (7-2) and the Angels' John Lackey (7-3).
Matsuzaka's teammates staked him to a big early lead with a four-run second inning against Rangers starter Brandon McCarthy, who threw 47 pitches in the inning. But after striking out Gerald Laird to end the bottom of the second, Matsuzaka grimaced and clutched his right side as he returned to the dugout.
"Before the game, he was feeling it," Red Sox manager Terry Francona said. "Then, in the second inning, he really felt it. I was kind of relieved, because it looked at first like he reached down for his hip or something.
"When he was throwing up, that was a pretty good indication he wasn't feeling too well. But he kind of gathered himself and went after it."
The Japanese pitching star sat in obvious discomfort and became physically ill between innings, but courageously pitched on. But he gave up the lead by allowing five runs in the fourth on Sammy Sosa's RBI double and two-run homers by Frank Catalanotto and Ramon Vazquez.
Under the circumstances, lesser teams might have decided it just wasn't their night. But the Red Sox yanked the lead right back in the top of the fifth on run-scoring hits by David Ortiz and Manny Ramirez. The rally began with a one-out single by Kevin Youkilis, who extended his hitting streak to 17 games.
"That was an important part of the game," catcher Jason Varitek said, "because the momentum had already swung their way."
The two runs off Texas reliever Wes Littleton (0-1) gave Matsuzaka a 6-5 lead and another chance to win. And after he escaped a two-on, none-out jam in the bottom of the inning, Francona decided Matsuzaka's 85-pitch effort was sufficient.
"He got through the fifth, and now it will be the most-covered case of intestinal turmoil I've ever seen," Francona predicted.
Pitching coach John Farrell said Matsuzaka was treated with fluids orally and with an IV, but did not appear to be facing a long-term problem.
"We have every reason to believe it's just a 24-hour type bug," Farrell said.
Matsuzaka did not speak with reporters after the game, but he issued a statement through a team publicist.
"I felt very good coming out of my warmups in the bullpen, and I was looking forward to pitching in this game," he said in the statement. "But, all of a sudden, I didn't feel too well.
"I tried my best to take the team as deep into the game as possible to fulfill my responsibility as the starter. I regret that I ended up being a burden on my teammates today. I'll do my best to prepare for my next start."
Varitek chuckled when told Matsuzaka had expressed shame over his illness. Was the pitcher being a bit hard on himself?
"Yeah, if he thinks he's a burden," Varitek said. "He was dry-heaving in the concourse. He battled. He got us as far as he could, and that was tremendous."
So, too, was the Sox's immediate response to losing the lead. After seizing the 6-5 advantage in the fifth, Boston put the game away with a four-run sixth against Rangers reliever Frank Francisco, who before Friday had allowed only four runs (three earned) in 13 appearances spanning 15 1/3 innings.
"We came right back at them the next inning, which is a good way to play the game," Francona said.
The Rangers mustered a final run in the seventh, when Kenny Lofton scored on Brendan Donnelly's wild pitch. It wasn't enough to change the expected result of a meeting between the team with baseball's best record and the club with the American League's worst.
Boston (32-15) has won six of its last nine games and 13 of 18, while the Rangers (18-30) have lost 12 of 17.
"We don't really think like that," Francona said. "We get consumed with who we're playing and we try to beat them. It doesn't really matter what their record is."