It was the second side session Gagne has had in the past three days.
Look for Gagne to be available for manager Terry Francona as early as Monday, when the Red Sox open a three-game series against the Devil Rays at Fenway Park.
"I didn't feel any stiffness," said Gagne. "I felt great. Day off tomorrow, and then start throwing in games."
There was great excitement when the Red Sox landed Gagne on July 31 in a trade with the Rangers. But the veteran closer struggled initially to acclimate to the setup role, and then he developed some mechanical flaws, while also tipping his pitches.
Gagne had just started to get things figured out at the time he developed right shoulder tenderness. In his last four outings before getting shut down, Gagne didn't allow a run.
"When my shoulder was starting to hurt a little bit, that's when I really figured out a lot of stuff," Gagne said. "It was unfortunate, but I had four or five good outings."
The last time he pitched for the Red Sox was on Aug. 26 against the White Sox.
"I'm just happy I'll be able to get some innings in the bullpen so they don't have to be overworked," Gagne said. "That's the most exciting part about it. You try to go out there and you can't give them your inning, because you're hurt, and then they put somebody else in your place and it takes a toll on the bullpen."
Backed by a commanding lead in the American League East standings and the advantage of roster callups, the Red Sox have been able to be conservative with Gagne's rehab program.
"I don't think they would have rushed me anyway, because they're really on top of everything here," Gagne said. "But that's all they said, 'We want you healthy. There's no need to push it.' I just need to go slow, and I don't know how to go slow. I just throw as hard as I can, and they pulled the rein on me. That was pretty good."
Isolated incident: It doesn't appear there will be any bad blood between the Red Sox and Orioles stemming from the unfortunate incident on Friday night, when Daniel Cabrera lost his cool and unleashed an upper-90s offering that went behind Dustin Pedroia's head. Even the Orioles seemed embarrassed by the pitch from Cabrera.
"I commend the Red Sox for keeping their cool last night," said Orioles manager Dave Trembley. "They had every reason to retaliate, and they didn't. That was smart on their part, because [Jon] Lester was pitching such a great game. Why turn that into something other than what's it's supposed to be -- that's a Major League baseball game."
Cabrera seemed incensed that he had balked in Coco Crisp from third, and his next pitch sent Pedroia scrambling. But why was Red Sox backup catcher Kevin Cash ejected along with Cabrera?
"I guess he was yelling out of the dugout," Francona said. "My back was to him, so I didn't see it."
Mirabelli still hurting: There's no word yet on whether backup catcher Doug Mirabelli (strained left hamstring) will be able to catch batterymate Tim Wakefield on Tuesday night.
"He's sore," Francona said. "Again, it's not like speed is a big part of his game. They've been treating him on and off during the game and again this afternoon. They'll keep doing it and see how he reacts."
In the meantime, Francona feels fortunate to have Cash in reserve. Unlike most catchers, Cash has proven adept at handling Wakefield's knuckleball.
"Sometimes you catch a break organizationally -- that he was willing to go to Triple-A to kind of helping develop [knuckleballer Charlie Zink] and play sparingly, but keep himself ready for something like this happening," Francona said. "There's guys out there, but not a lot of them, that can do it and do it the way he did. This kid gives us a little jolt of energy. He's got a good edge to him when he's catching. Even when he's not catching, it's been good for us."
Papelbon simply unhittable: Forgive the Red Sox if they start packing up the dugout the second closer Jonathan Papelbon enters a game.
Papelbon has retired the last 15 batters he's faced. He hasn't given up a hit since Aug. 17. And since surrendering a game-tying home run to the Rays' Jonny Gomes on the night of July 28, opponents are just 1-for-45 against Papelbon.
Opponents are hitting .135 against Papelbon this season, which is on pace to be the second stingiest in Major League history among pitchers with at least 50 innings.
So who holds the record? It's Papelbon's setup man Gagne. In 2003, he limited hitters to a .133 batting average as the Dodgers closer.
Coming up: Ace Josh Beckett (17-6, 3.30 ERA) will continue his push for the AL Cy Young Award when he faces right-hander Jeremy Guthrie (7-5, 3.65) in the finale of this four-game set on Sunday afternoon. First pitch is scheduled for 1:35 ET.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.