Felix Doubront (7-4) gave up three runs and six hits. He walked two and struck out six in 6 2-3 innings. It was his 13th straight game allowing three runs or fewer, the best stretch by a Red Sox left-hander since at least 1920.
"The bottom line is we're still in first place," Doubront said. "That's how I look at it. Give credit where credit is due. David Price pitched a great game."
Boston lost for the fifth time in 15 games against the Rays.
Tampa Bay jumped ahead with three runs in the third on Myers' two-run single and Sean Rodriguez's sacrifice fly. Myers' bloop fell into shallow center after the Rays loaded the bases on two singles and a fielder's choice.
In the seventh, Napoli homered over the seats above the Green Monster and out of the park.
Loney and Jose Molina each had RBI singles off Matt Thornton to push the Rays' lead to 5-1 in the eighth.
Like in the opening game of the series when left-hander Matt Moore threw a two-hitter in a 3-0 victory, the Red Sox had trouble stringing hits together.
In the fifth, Napoli had a leadoff double, but the next three hitters flied out. Boston also had leadoff singles in the second and fourth, but Price retired the side easily both times.
Doubront had been 3-0 with a 1.83 ERA in his previous six starts, allowing two earned runs or fewer in all of them.
NOTES: Maddon juggled his lineup, moving Evan Longoria up to the No. 2 spot. "Hopefully he'll see a different type of pitching," Maddon said. Longoria had homered in three of his previous five games, but hit just .136 in his previous 18 with one homer. Maddon inserted hot rookie Myers in the cleanup spot. ... Boston sends John Lackey (7-7, 2.95 ERA) against Tampa Bay's Jeremy Hellickson (9-3, 4.62 ERA) in the series finale on Thursday. ... Rays highly touted prospect RHP Taylor Guerrieri underwent ulnar collateral ligament surgery on Wednesday in Pensacola, Fla. He is expected to miss the rest of this season and part of next season.