HOUSTON -- The Boston Red Sox spent the first six games of this road trip struggling on offense.
They've busted out of that slump since coming to Houston.
Boston has scored 17 runs in the last two games after managing just 15 in the previous six games.
Red Sox manager Terry Francona said figuring out why a team goes through spans where it struggles to score runs is difficult.
"That is why when you are not scoring, you don't have to like it, but you don't need to panic, you don't need to change things up, you just keep running them out there, because they are good hitters," he said. "You are going to go through periods where it just doesn't work."
Navarro hit a solo shot in the seventh for his first major league homer. McDonald's drive in the eighth landed on the train tracks atop the wall in left field and stretched the lead to 9-3.
McDonald was in a 3 for 34 slump before the home run.
"I know things are going to turn around for me," he said. "I'm working hard. I've been feeling good at the plate, I just haven't been getting results. So it feels good to get rewarded with the home run, but the main thing is just getting something positive going."
One night after rallying for six runs in the seventh inning of a 7-5 victory over the Astros, the Red Sox got off to a fast start against J.A. Happ.
Adrian Gonzalez had an RBI single and David Ortiz, playing first base in the NL park, walked with the bases loaded to force in another run as Boston jumped out to a 3-0 lead in the first inning. Pedroia added a run-scoring double in the fifth.
That was more than enough for Andrew Miller (2-0), who yielded two runs and seven hits in six innings.
Happ (3-10) left with two outs in the seventh and was charged with five runs and seven hits. He has dropped a career-worst six consecutive decision and Houston has lost his last nine starts.
"They're tough," Happ said. "They're a good ballclub. They pitched better, hit better and played better defense than we did. That's why they won."
"We battled them, we hit the ball hard sometimes," Bourn said. "We could've gotten a break, that could've started something. Other than that, we've got to find a way to just learn. That's it."
Navarro, who was called up from Triple-A Pawtucket before Thursday's game, hit his homer to the first row of the Crawford Boxes in left field with one out in the seventh. It was the second pinch-hit homer by a Red Sox player this season.
Navarro had some trouble getting onto the field before his homer.
"I couldn't find my helmet," he said in Spanish. "(Francona) was like, 'Let's go, you are up next.' I just took somebody's."
Boston reliever Alfredo Aceves gave up consecutive singles to pinch-hitter Jeff Keppinger and Bourn with two outs in the bottom half before walking pinch-hitter Matt Downs. He was replaced by Daniel Bard, who walked in a run before retiring Carlos Lee to limit the damage.
Boston started the eighth inning with three consecutive singles and Jarrod Saltalamacchia's sacrifice fly made it 6-3.
Bourn extended his hitting streak to 11 games with a leadoff triple in the first. Angel Sanchez drove him in with a single.
"For Andrew, it was a tough first inning," Francona said of Miller. "It did not look like he had a ton of velocity, and they really hit some balls hard. But he got out of it with just one. He settled down."
Ortiz, normally the designated hitter, played first and Gonzalez moved to right field to start Saturday's game. Gonzalez moved to first in the bottom of the sixth when Josh Reddick replaced Ortiz. Gonzalez's start in right field was the third appearance of his career at a position other than first base or designated hitter.
Miller was struck on the back by a ball hit by J.R. Towles in the fifth inning. Trainers talked with him for a couple of minutes before he threw a warmup pitch and remained in the game.
Red Sox OF Jacoby Ellsbury returned after sitting out Friday's game due to illness. "I don't think he feels great," manager Francona said, "but he's good enough to play." ... Boston OF Carl Crawford jogged in the outfield and took batting practice, as he continues to recover from a strained hamstring. Crawford is due to come off the disabled list on Sunday, but Francona said Crawford isn't ready to play just yet. "He's building," Francona said, "and it was a really productive day."