The Rangers farmhand fell a triple shy of the cycle and drove in three runs, while Red Sox prospect Bryce Brentz chipped in a pair of RBIs as Surprise beat Peoria, 8-4, for its first win of the season.
McGuiness, who had 23 homers and 77 RBIs for Double-A Frisco this year, went 4-for-5 with an RBI double in the third inning and a two-run homer in the fourth a day after going hitless in his AFL debut.
"[The pitches] just seemed to hit my barrel," he said. "Yesterday was a real rough game; my timing is all messed up. The ball looks like a golf ball coming in there. You're just looking to swing early, and that's what happened today. I was able to get some good swings on it.
"That's just baseball. You come out one day and put up a goose egg, then the next day you come out and the hits start falling for you."
Selected by the Red Sox in the 13th round of the 2009 Draft, McGuiness established career highs in his fifth Minor League season and third in the Texas organization.
The 24-year-old said that facing elite pitching on a daily basis -- especially after nearly a month off -- will be the biggest challenge he faces in the Fall League.
"These guys are tough to hit off even when you're game-ready in the middle of the season," McGuiness said, "so it's going to be a big adjustment. But we have a real good team; all of these guys are out here because they can play."
Brentz, who tripled and scored a run on Opening Day, was credited with an RBI in the third when he reached on a botched double-play grounder. He delivered an RBI single an inning later.
Boston's No. 4 prospect batted .290 with 17 homers and 76 RBIs in 127 games between Double-A Portland and Triple-A Pawtucket this season.
Cardinals outfield prospect Colin Walsh scored twice and gave the Saguaros a 5-1 lead with a two-run double in the fourth.
Boone Whiting (Cardinals) started for Surprise and allowed a run on three hits over two innings.
First-round pick Mike Zunino, the Mariners' No. 4 prospect, blooped an RBI single in the Javelinas' three-run seventh, but the rally came up short.
Reds right-hander Tim Crabbe was charged with two runs -- one earned -- on four hits and a walk over 2 1/3 innings in his first start for Peoria.
Danny Wild is an editor for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.