The Sounds were coasting with a 5-1 advantage until starter Richie Gardner and all three relievers gave up runs as Round Rock posted a 10-5 victory.
Gardner allowed four runs on seven hits, while left Randy Choate, still on a rehab assignment, was handed the loss after giving up two hits, a walk and three runs in his only inning.
Gwynn connected on his first homer of the year with two on and two out during the hosts' five-run fourth inning to finish with three RBIs.
One night after a scintillating 10th-inning victory, the Stars managed only four hits in falling 5-0 against Birmingham.
Cole Gillespie, who won Friday night's contest with a solo homer, tripled and finished 1 for 3, but Huntsville had only three other singles.
Mike Jones, despite allowing only three hits, one walk and one run during the first five innings, was tagged for the loss and fell to 0-3.
The Manatees, who trailed 4-2 after scoring in the sixth, rallied for two runs in the bottom of the ninth against Daytona. Then the Cubs tallied once in the 11th to claim a 5-4 victory.
Righty starter Joshua Butler suffered one bad inning out of seven, allowing four of the six hits he gave up plus a walk as Daytona scored four runs in the fourth. Travis Wendte and E.J. Shanks each pitched a scoreless inning before Mike McClendon (2-4) suffered the setback.
Right fielder Lorenzo Cain, catcher Jonathan Lucroy and third baseman Taylor Green led the way with two hits apiece while the latter contributed two RBIs. Second baseman Jimmy Mojica scored twice, including on his solo homer in the third.
The first-place Power jumped out to a 2-0 first-inning lead and then pulled out some heroics with the winning run in the 10th for a 3-2 decision against second-place Hagerstown to improve to 11-5 in the second half.
Righty Evan Anundsen was masterful through the first five innings, allowing only two hits and a walk before the Suns notched two tallies in the sixth. Lefty Mike Ramlow (3-3) followed with 4.1 innings of two-hit, scoreless baseball to get the win.
West Virginia mustered only five hits, four singles and first baseman Curt Rindal's double.
The Brewers grabbed a 5-1 margin in the fifth and got superb relief pitching, claiming a 5-3 triumph against first-place Billings.
Starter Wily Peralta tossed hitless ball during his three-inning stint, Mark Willinsky gave up one run in two innings and Brandon Ritchie fired 3.2 scoreless innings before giving up two runs with two outs in the bottom of the ninth. Adam Arnold entered and got a strikeout for the third out to record his fourth save.
The Brewers (2-9) finally tasted victory again, scoring seven runs in the first three innings en route to a 9-3 triumph over the Royals that snapped their six-game losing skid.
Right-hander Adrian Rosario (1-0) went the first six innings, allowing three runs on six hits and a walk while striking out four. Signed as an undrafted free agent in 2006, Rosario was 3-3 last year in Arizona and was making his second start and third appearance of the year.
The Brewers' hitting stars included first baseman Pedro Ramos (3 for 5) and designated hitter Shawn Zarraga (3 for 4). Ramos and Zarraga each chipped in one of the team's four doubles and knocked in two runs apiece.