Kyle Ross-USA TODAY Sports

Bryce Harper hasn't played in the field in a week, but the two-time MVP has definitely made his presence known at the plate.

Harper could serve as the designated hitter for the sixth straight game on Sunday when the Phillies aim for a three-game sweep of the visiting St. Louis Cardinals. He had three hits and two RBIs in Philadelphia's 12-1 victory on Saturday.

The Phillies have been exercising caution with Harper, who has played first base only five times over the last 14 games. Philadelphia manager Rob Thomson said Harper is being kept off the field for precautionary reasons while dealing with back tightness.

"I'm progressing well," Harper said. "I just didn't want to take a backward step and not be able to play this coming week. So it's getting better."

Harper is 17-for-34 with five homers, 11 RBIs and 12 runs in his last nine games for Philadelphia, which has outscored St. Louis 19-3 in the first two games of the series.

The Phillies continued their power surge on Saturday with homers by Bryson Stott, Nick Castellanos and Brandon Marsh. Philadelphia has gone deep 48 times in August, setting a franchise record for home runs in a month.

St. Louis third baseman Nolan Arenado sat out Saturday's contest after leaving Friday's series opener with lower-back tightness. The eight-time All-Star is listed as day-to-day.

"If I feel good, I'm going to be out there," Arenado said.

Cardinals left-hander Drew Rom (0-1, 14.73 ERA) is set to make his second career start in the series finale.

Rom yielded eight runs (six earned) over 3 2/3 innings in an 11-1 loss to the Pittsburgh Pirates last Monday. The 23-year-old struggled to recover from a rough first inning that included a costly error by second baseman Jose Fermin.

"I'd like to definitely see him again," St. Louis manager Oliver Marmol said of Rom. "I think it will show better than what we saw. (From) a confidence standpoint, get out of that first inning, walking off and feeling good about it. Does the line look good at the end of the game? No. Do I think his stuff will play better at this level? I think it will, yeah."

Philadelphia will counter with right-hander Aaron Nola (11-8, 4.49), who allowed two runs over seven innings in a 10-4 win over the San Francisco Giants last Monday.

Nola, 30, owns a 3.49 ERA in 11 home starts this season compared to a 5.26 mark in 15 outings away from Citizens Bank Park.

Paul Goldschmidt is 3-for-20 (.150) with eight strikeouts against Nola, who is 5-3 with a 2.69 ERA in nine career starts versus St. Louis.

Philadelphia has won four of its last five games with everyone contributing throughout the lineup. Marsh is 12-for-26 (.462) during his career-high nine-game hitting streak.

"(Marsh is) swinging at good pitches, so he's not chasing, and he's using the entire field," Thomson said. "And that's usually (what causes) every hitter's success, but that's what he's doing right now."

The Phillies have also received a spark from shortstop Trea Turner, who extended his hitting streak to seven games with two hits on Saturday.

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