His spot in the rotation will be filled by a pitcher who has exasperated Boston fans for years.
Bard's conversion from reliever to starter has been a rocky one, and he was shipped to Triple-A Pawtucket this week after walking six and hitting two batters in 1 2-3 innings Sunday at Toronto.
The Red Sox (29-29) may have been more comfortable sending him down knowing Matsuzaka was ready to return almost exactly one year after elbow surgery.
Expectations are uncertain for the Japanese right-hander, who is in the final season of a six-year, $52 million contract he signed after the Red Sox paid a $51.1 million posting fee and brought him to Boston with great fanfare.
Matsuzaka has shown flashes of brilliance but has been mostly inconsistent, walking 4.4 per nine innings for the majors' fourth-highest rate since he entered the league in 2007.
He was 3-3 with a 5.30 ERA in eight outings - seven starts - before his injury last year, walking seven in his most recent big league outing May 16, 2011.
"It's hard to predict what's going to happen," manager Bobby Valentine told his team's official website. "I hope he throws strikes, and I hope he has more than two pitches to do it with, and I'd be happy if that happened."
Matsuzaka seems happy to be returning, but admitted he may have trouble harnessing his emotions.
"Saturday's game will be a special game. It will present a new step for me," Matsuzaka said. "It is going to be a very emotional day, but I have to remain calm and treat it like any other start I've had throughout my career."
Keeping pace with Gonzalez (7-2, 2.31 ERA) will likely present a tough task.
The left-hander has a 1.87 ERA in his last 10 starts even though he wasn't sharp Sunday against Atlanta, allowing three runs, seven hits and three walks in 4 2-3 innings of a 3-2 loss.
"I was falling behind on guys," Gonzalez said. "I just couldn't get it in there. Hopefully I turn that around next start."
He made five starts against Boston during his AL days with Oakland, winning two of his last three but posting a 5.79 ERA overall. Kevin Youkilis has six hits including a homer in 11 career at-bats against him.
Gonzalez, though, leads all major league starters this season with a .172 opponent batting average and ranks second with 11.4 strikeouts per nine innings - falling behind teammate Stephen Strasburg in that category after Strasburg struck out 13 in Friday's 7-4 win.
The NL East-leading Nationals (33-23) got the franchise's first-ever victory at Fenway Park with plenty of help from Bryce Harper.
The rookie went 3 for 5 with a homer, a double and three RBIs. He's hitting .354 with four homers, three triples and 12 RBIs in his last 16 games.
"It's an unreal experience, coming in and playing for the first time at Fenway," Harper said. "It was so much fun. They just have a great fan base and it's just great to play here."
Boston lost for the fourth time in five games but may have been encouraged by Adrian Gonzalez's performance. He hit the fifth homer of his disappointing season and has five hits in his last two games, although he's gone 93 at-bats since his last walk May 15.
- Daisuke Matsuzaka
- Gio Gonzalez
- Washington Nationals
- Daniel Bard