"It's a confidence booster, to show that I can still belong here and attack these guys," said Nuno, who retired 10 straight through one stretch and exited to a standing ovation from a sellout crowd of 48,522.
Kelly Johnson and Brett Gardner hit back-to-back home runs off Red Sox starter Brandon Workman, and Brian McCann added a long two-run shot off Craig Breslow as the Yankees won their second consecutive game.
"Obviously a good thing," said Johnson, who snapped an 84 at-bat homerless stretch with his first blast since May 3. "We scored a lot of runs. One was all we needed."
Girardi bristled in a pregame news conference when he was quizzed on the decision to stick with Nuno, who was hammered in his previous two outings and has struggled mightily at Yankee Stadium, where he compiled a 7.09 ERA coming into Friday's effort.
Nuno's excellent 91-pitch outing provided Girardi with a prime opportunity to gloat, though he did not snap up that bait. Rather, Girardi acknowledged that while Nuno may not possess electric stuff, he seems to have the guile to keep big league hitters off-balance.
"He fights," Girardi said. "It's not a guy that throws 95 [mph], not a guy with a wipeout slider. It's a guy that just goes out and competes and finds a way to get it done. He's beaten a lot of the odds, in a sense."
Nuno walked two and struck out five, authoring another chapter of frustration for the Red Sox, who entered play on Friday ranked third to last in the American League in runs scored.
"We felt like, coming into this ballgame, we had a chance to do something against their starter, but he made some pitches against us," Red Sox manager John Farrell said.
New York's bullpen was stellar. Dellin Betances provided 1 1/3 innings of scoreless relief before turning over duties to Adam Warren in the eighth, and Matt Thornton worked the ninth to preserve Nuno's second win of the year and his first since May 7.
In his most recent outings against the Athletics and Orioles, Nuno said that he had been trying to overpower his pitches, leaving balls up in the zone that were hit hard. He credited McCann's game-calling for Friday's bounceback, saying that he did not shake off a single sign from the veteran catcher.
"I really don't shake," Nuno said. "I just trust him."
"He really answered the bell tonight," McCann said. "He came out, established the strike zone, established what he wanted to do and got big outs after big outs."
New York produced four runs in seven innings against Workman, who returned from a six-game suspension to make Friday's start.
The Yankees gave Nuno a quick lead in the first inning as Derek Jeter singled in his first at-bat as a 40-year-old, moved to third base on Jacoby Ellsbury's double and scored on a Mark Teixeira sacrifice fly.
Johnson connected for a two-run homer to right field off Workman in the fourth and Gardner followed with a full-count blast that also found the right-field seats, marking the fourth time this season that the Yankees have hit back-to-back home runs.
In the eighth, McCann teed off for his ninth homer of the year, which landed in the second deck in right field.
"I got a 3-1 fastball, kind of in the middle, and was able to drive it, which I haven't been able to do a lot of," McCann said. "So that was good -- to actually drive a baseball."
Girardi saw the power display as a reason for the club to have faith that the offense will come around.
"I believe they're going to come," Girardi said. "We went through some times that we were up and down, but I really believe that these guys are really going to contribute and put up numbers."