It was the first career homer at Fenway Park for the former top Red Sox prospect, who played three seasons with the team before being dealt to Detroit on July 30, 2013, in a three-way trade that brought Jake Peavy to Boston.
Justin Verlander (10-6) earned his first win at Fenway in nearly seven years, holding the hot-hitting Red Sox to one run on five hits and two walks with five strikeouts in six innings.
The 2011 American League MVP and Cy Young Award winner hadn't won at Fenway since striking out eight over four scoreless innings in a 2-0 victory Aug. 13, 2009.
Travis Shaw and Sandy Leon drove in runs for Boston (55-42), which fell for the third time in four games and saw its 15-game homer streak snapped.
Drew Pomeranz (0-1) fared better in his second start with Boston, lasting six innings while allowing two runs on four hits and two walks with seven strikeouts.
The first-time All-Star went 8-7 in 17 starts with San Diego before the July 14 trade that sent him to Boston.
Joe Kelly relieved Pomeranz, making his first appearance since being recalled from Triple-A Pawtucket on Sunday. The flame-throwing right-hander consistently touched 100 mph with his fastball. Kelly gave up one run on two hits in an inning after not pitching in the major leagues since June 1.
Shaw's line-drive double allowed Jackie Bradley Jr. to score from first base in the second inning, opening the scoring.
Iglesias finally got to Pomeranz in the sixth, crushing an 0-1 fastball clear over the Green Monster in left. It was his fourth homer of the year and first since June 28.
McCann and Martinez added insurance runs with RBI singles in the seventh and eighth, respectively.
Boston's Bryce Brentz entered as a pinch hitter in a golden opportunity with the bases loaded and no outs in the eighth, but he struck out swinging.
Leon singled up the middle in the next at-bat to plate a run, but Brock Holt struck out looking and the Tigers brought on Francisco Rodriguez.
The Detroit closer got Mookie Betts to ground out to end the threat, then pitched a scoreless ninth for his 28th save.
NOTES: Boston RF Mookie Betts returned to the lineup after missing two games with right knee soreness. He went 0-for-5. ... Detroit optioned RHP Buck Farmer to Triple-A Toledo. Farmer was the 26th man in Sunday's doubleheader. ... Red Sox RHP Craig Kimbrel (left knee medial meniscus tear) threw a good and aggressive 25-pitch bullpen session Sunday, manager John Farrell said. ... Boston 1B Hanley Ramirez was selected the American League Player of the Week for July 18-24 after batting .333 (7-for-21) with five home runs and 12 RBIs in six games. Ramirez hit a trio of two-run homers Wednesday and had three-run blast on Saturday and Sunday. ... Red Sox president of baseball operations Dave Dombrowski reflected on the end of his 14-year tenure as the Tigers' general manager. "We didn't worry really very much about upcoming years," he told the Boston Herald. ... Tigers RHP Mike Pelfrey (3-9, 4.78 ERA) opposes Red Sox RHP Steven Wright (12-5, 2.67 ERA) Tuesday.