"My approach isn't going to change, just square up the ball and work the counts," Dominguez said. "There might just be some more runs up for grabs."
With catcher and cleanup mainstay Jason Castro out of the lineup on Sunday, Porter said he was looking to get another RBI threat near the top of the order.
"We're facing a lefty and Jason Castro isn't playing," Porter said. "When you look at the dynamic of who's in the lineup, [Matt] is one of the better run producers and that's why he's hitting fifth out there."
Dominguez has made a pinch-hit appearance at both the No. 2 and No. 5 holes this season, recording a hit on July 9 against St. Louis in his only time hitting fifth this season.
Still, he's no stranger to the top of the order, batting fifth or higher in the lineup 11 times over the final month of the 2012 season. During those games, he hit .233 (10-for-43) with three home runs and nine RBIs.
As for whether a repeat of last season's late top-of-the-order surge is in the cards, Dominguez wasn't sure.
"It all depends on how I'm swinging the bat, what the matchup is that day," he said. "I'll try to make it easy to write me in up there, but I'm not worrying about it."
Chris Abshire is an associate reporter for MLB.com.