DETROIT -- Brennan Boesch wasn't fazed by the rain -- or the unfamiliar reliever on the mound.
Adams (0-1) was making his debut for the Rangers after coming over from San Diego just before the trade deadline. He got the first out of the eighth, but as the weather took a brief turn for the worse, Boesch lined his 16th homer of the season over the wall in right field.
"I had no idea who he was," Boesch said. "No disrespect to him, but he's not in our league and he just got traded over here."
Jose Valverde pitched the ninth for Detroit, earning his 29th save in 29 chances.
Detroit now leads second-place Cleveland by three games in the AL Central.
Lewis allowed five runs -- four earned -- and 10 hits in four-plus innings. He walked three and struck out three.
Cruz started the Texas rally in the eighth with his 24th homer, and after a walk to Mitch Moreland, Napoli tied it with his 16th homer.
With the rain suddenly picking up, Boesch broke the tie with one swing.
"In the minor leagues, it seemed like I played in rain all the time in Erie and Toledo, for a little bit," Boesch said. "You just have to focus that little bit more."
Adams had a 1.13 ERA in 48 innings with the Padres this season, but his first appearance for Texas was forgettable.
"I left a changeup up and he hit it out of the park," Adams said. "I have the desire to do good and impress these guys. Maybe I was trying to do it too much."
Ian Kinsler nearly brought Texas even again in the ninth, hitting a long foul ball on Valverde's first pitch, but the Rangers couldn't score. Valverde got Cruz to fly out to left with two on to end it.
Detroit led 2-0 after RBI singles by Wilson Betemit in the second and Victor Martinez in the third. After Cruz hit an RBI single in the fourth for Texas, Avila hit his 11th home run, a towering fly through the rain that barely cleared the wall in right-center.
Betemit followed with a single, and Lewis compounded his problems by throwing high to first base for an error on Austin Jackson's routine bunt. The Rangers escaped further damage in the inning thanks to a nice play by shortstop Elvis Andrus, who ranged well to his right to field Boesch's grounder and threw to third for a force play.
Texas scored in the fifth on Yorvit Torrealba's RBI single and had runners on first and second with nobody out when Andrus popped up a bunt.
"That was a huge momentum turn in the game," Scherzer said. "To be able to finish off that inning and keep it at 3-2 was just good momentum for our team."
Avila's bases-loaded single in the bottom of the inning brought in two more runs and made it 5-2.
The Tigers might have scored more, but they hit into three double plays in the first five innings.
"We probably could have had a way bigger lead with the way we were swinging the bats, getting hits, but we just weren't driving in runs," Boesch said. "You don't want that to come down to it like it did, but it worked out for me and the team, so I'm happy."
Texas 3B Adrian Beltre, on the DL with a strained left hamstring, took batting practice on the field before the game. ... Josh Hamilton slid feet first into home to score the first Texas run. He broke his arm diving head first toward the plate at Detroit in April. ... Peralta made a sprawling stop at shortstop on Kinsler's grounder in the seventh. ... The Rangers made three errors. ... Lewis has allowed 27 HRs this season. ... RHP Doug Fister, acquired over the weekend in the same trade that brought Pauley to Detroit, will make his first start for the Tigers on Wednesday night against LHP Matt Harrison of the Rangers. ... The Tigers have won 15 of their last 18 games against Texas at Comerica Park. ... Harrison has a 2.16 ERA in his last 12 starts. ... Fister is 3-12 but has a 3.33 ERA on the year.