CLEARWATER, Fla. -- If the Phillies need Zack Wheeler to pitch for them on Opening Day, he will be ready.

He flashed some of his electric stuff Tuesday at Spectrum Field, allowing four hits, one run, one walk and striking out six in four innings in a 5-1 victory over the Twins. Aaron Nola missed Monday’s start because of the flu, which could bump him from his anticipated season-opening outing, on March 26 in Miami. Phillies manager Joe Girardi said Nola felt better Tuesday. He could throw a bullpen session Thursday and pitch a simulated game Saturday.

“That’s kind of our hope,” Girardi said.

Girardi said in that scenario, Nola still could pitch on his previously scheduled regular-season debut (nobody has officially said Nola will pitch Opening Day). If Nola is not ready, Wheeler could move up one day and pitch instead.

“If they need me, whenever they need me, I’ll be ready,” Wheeler said.

Tuesday provided a glimpse at what the Phillies rotation could look like in the future. Wheeler signed a five-year, $118 million contract in December. He impressed in his four innings. He struck out the side swinging in the first, including Twins catcher Willians Astudillo, who has struck out just 11 times in 301 career plate appearances.

Top pitching prospect Spencer Howard made his Grapefruit League debut in the eighth. He allowed two hits and struck out one in a scoreless inning, throwing 17 pitches (12 strikes). Howard is the No. 34 prospect in baseball, according to MLB Pipeline.

The Phillies have brought Howard along slowly this spring. He threw only 91 1/3 innings last season, including the Arizona Fall League, so the organization is trying to monitor his workload. In a perfect world, Howard is pitching well and has enough innings left to help the Phillies make a push for the postseason in the second half.

Howard is a potential difference maker.

“Obviously you really get excited about that arm,” Girardi said. “His ability to pitch deep into games, swings and misses. I've watched his bullpens and they've been good and crisp. For him to be able to carry it out here his first time, that's a positive.”

Howard allowed a single to Brent Rooker and a one-out single to Astudillo to put runners on first and second. But he got Jimmy Kerrigan to fly out to right field and he struck out Wilfredo Tovar looking on a fastball away to end the inning.

“It felt good,” Howard said. “A little jumpy, too much energy towards the beginning, but I got in a groove near the end and felt good, overall. I feel healthy.”

Howard watched Wheeler pitch beforehand. He smiled when asked what it might be like to be pitching together at some point.

“It’s crazy,” he said. “He’s obviously really good. His fastball is explosive. His changeup is good. His curveball is good. Everything is good. He locates well. What else can I say? Yeah, it’s good. … Just watching how [the other starters] go about their business and their preparation, more than anything has been the biggest takeaway for me. I’ve said it before, but it’s not an accident that they’re big leaguers. Their work proves it.”

Tuesday’s effort was just one inning, but it was one step closer to the big leagues for Howard. It feels a little closer now.

“Yeah,” he said. “Just getting out here. What was it? 7,000 people? It’s still not anything like Philly, but the energy is there.”