Melvin replaced Bob Geren earlier in the day, but the change couldn't keep Oakland from its 10th consecutive defeat.
Mark Buehrle (6-4) threw seven strong innings and improved to 5-1 with a 3.00 ERA in his past seven starts. He allowed seven hits and three runs for the White Sox, who have won six of their past nine and 20 of 32.
|More on A's at White Sox|
Bob Melvin is stepping in at the right time to save the A's. Read More >>
Dunn was back in the lineup after sitting out two games because of a miserable start in which he has hit. 176. He was hit by a pitch and scored in Chicago's three-run second. He connected for the first time since May 24, a two-run shot in the third.
Trevor Cahill (6-4) lasted only 2 2/3 innings, his shortest outing of the season. He was unlucky to an extent, allowing four infield hits on dribblers in front of the plate. But he also walked three, hit a batter and allowed Dunn's two-run blast.
It was a rocky introduction for Melvin, who went 493-508 in previous managerial stops in Seattle and Arizona. The Athletics, who entered last in the AL with 223 runs scored, scored three runs or fewer for the fifth consecutive game, and eighth time during their skid. Oakland last lost 10 straight from July 28-Aug. 7, 2008.
In the second, the White Sox loaded the bases on A.J. Pierzynski's walk, Alex Rios' single and Dunn's hit by pitch. After Oakland third baseman Adam Rosales dropped a foul pop, Omar Vizquel hit a sacrifice fly to right to plate Chicago's first run.
Gordon Beckham reached on a tapper in front of the plate, reloading the bases. Juan Pierre walked in a run, and then Alexei Ramirez hit a dribbler up the third-base line that Cahill was unable to handle, scoring the inning's third run.
As maddening as that inning was for Cahill, the third was more of the same -- at least after Dunn's two-run shot to barely cleared the left-field fence for his sixth homer of the year.
Vizquel followed that with another short dribbler to reach first. Beckham singled and Pierre reached on yet another infield hit to load the bases. Ramirez drew a walk to score Vizquel, a fitting end to a frustrating night for Cahill, who gave way to reliever Bobby Cramer.
Cahill is now 0-4 in his past six starts.
Meanwhile, Buehrle allowed Rosales' run-scoring single in the second, the last of three straight singles for Oakland. He then settled down to throw 4 2/3 scoreless innings, allowing only a walk and an infield single in the third.
Oakland rookie Jemile Weeks drove in his first career run on a bloop single in the ninth.
- Quentin extended his hitting streak to 11 games, while Konerko extended his to 10.
- Dunn's home run was the 360th of his career, breaking a tie with Johnny Mize for 74th on the career list.
- Saying he was glad to be back in the lineup, Dunn said that during his rest he learned "[I] don't like sitting out." Manager Ozzie Guillen had a request for Dunn: "I asked, 'Could you please have a good day so then they don't have to ask me anymore questions about you? Please have a good day so [hitting coach] Greg Walker doesn't have to drink a bottle of wine to forget about your bad night?' "
- The game was the 1,200th for Guillen, who began the night with a 630-569 record. He is tied with Boston's Terry Francona for the fourth-longest current tenure as manager with one club, behind St. Louis' Tony La Russa (1996), the Los Angeles Angels' Mike Scioscia (2000) and Minnesota's Ron Gardenhire (2002).
- Chicago improved to 136-135 at home against Oakland.
- Graham Godfrey will start for Oakland on Friday in his big-league debut.