WASHINGTON -- Dan Haren won his third straight start and first baseman Adam LaRoche had RBI singles in the first two innings as Washington beat Detroit 5-4 on Thursday to sweep the two-game series between preseason playoff favorites.
LaRoche, whose batting average was below .160 in April, has now hit in six games in a row and was 9 for 15 in his past five games before he struck out in his last two at-bats Thursday.
The Tigers (19-13), who open a series at home on Friday with Cleveland, had never lost to Washington in six tries before Wednesday.
Haren (4-3) allowed four runs in six innings as Washington (19-15), which begins a home series with the Chicago Cubs on Friday, won for the sixth time in seven games. Rafael Soriano pitched the ninth to get the save for Washington, who also got one scoreless inning from Ryan Mattheus and Drew Storen out of the bullpen.
Detroit pulled to 5-4 on a three-run pinch-homer against Haren in the top of the sixth by Matt Tuiasosopo, who was signed by the Tigers as a minor-league free agent before the season. It was his first career pinch-homer and the first for Detroit since Alex Avila went deep against the White Sox in 2011.
The Nationals scored two runs in the second to take a 5-2 lead as Ryan Zimmerman and LaRoche had RBI singles off Detroit starter Doug Fister (4-1), who was bidding to start 5-0 for the second year in a row.
The right-hander lasted just three innings and gave up five runs (four earned) and eight hits. Fister was replaced in the fourth by Darin Downs, a left-hander who pitched two scoreless innings before Luke Putkonen came on in the sixth.
Detroit had cut the lead to 3-1 in the top of the second as Fister had an RBI single to score Jhonny Peralta, who had singled with one out and gone to third on a single by Omar Infante.
Peralta has a hit in 21 of his last 24 games. He had hits in his first two at-bats on Thursday and then walked in the sixth against Haren. Infante singled in his first three at-bats before he fanned in the eighth against Storen.
Washington scored three runs in the first with an RBI fielder's choice by Bryce Harper and RBI singles by LaRoche and Ian Desmond.
Haren allowed four homers in his first start for Washington on April 5 against the Cincinnati Reds. But in his last start, he gave up just one run in eight innings in a win May 2 at Atlanta. He is now 5-4 against Detroit.
Haren entered the game with a 1.76 ERA since the start of the 2008 season against the Tigers, the best mark of any pitcher with at least four starts against Detroit.
NOTES: Right fielder Jayson Werth, bothered by a sore hamstring, was not in the starting lineup for the Nationals. He has not played since May 2. ... The hit by Fister was the third of his career and just his second RBI. His first start at Nationals Park came when he played for Seattle. ... Washington entered the game with a 1-6 lifetime record against the Tigers -- the last team the Nationals defeated since moving to the nation's capital in 2005. ... Haren entered the game with a 5.01 ERA and Fister had a 2.48 ERA. ... Washington pulled off a made-for-TV blooper in the top of the fifth as Haren caught a liner off the bat of Torii Hunter. Austin Jackson was way off second, but the throw by Haren went between Desmond at short and second baseman Danny Espinosa into center field, but Jackson could not advance.