Texas won its sixth straight, became the first American League team to reach 10 victories this season and then headed off to Detroit for a four-game battle against the team it eliminated in last year's AL Championship Series.
For the second straight evening, the Red Sox took an early 2-0 lead, but Texas went in front 3-2 on Napoli's fourth-inning blast. He hit a pair of two-run homers Tuesday in the Rangers' 18-3 clubbing of Boston.
Napoli added a two-run double to finish off a three-run eighth.
Derek Holland (2-0) earned the win, going seven innings while giving up two runs on four hits with seven strikeouts. No Texas starting pitcher has suffered a loss this season and the five-man rotation has a combined ERA of 2.44.
Josh Beckett (1-2) took the loss, surrendering three runs on seven hits in seven innings.
Kevin Youkilis gave Boston the early lead with a two-run shot in the second.