PORT ST. LUCIE, Fla. -- Jonathon Niese spent a simulated game Thursday trying to get his mechanics back in order.

Niese said he noticed in his last bullpen session that his right leg was stepping toward the first-base side -- not directly at the plate -- as he landed. That caused him to throw across his body and, he believes, fatigued his left shoulder.

During a 76-pitch session Thursday against New York Mets batters, Niese concentrated on striding longer and toward the plate. He suggested that helped his shoulder feel better.

"It actually felt a lot better," Niese said. "I wasn't fatigued at the end."

Niese had been scheduled for the evening Grapefruit League game against the Washington Nationals in Viera, but was moved up to the 10 a.m. simulated game because of a rainy forecast. Prospect Matt Bowman instead will face the Nats at 5:05 p.m. ET.

"Games like these, all you're doing is getting your workload in, getting the volume up," Niese said about the simulated game. "You're working on your pitches, but the results you really don't care, because you're facing the same three or four guys at a time."

Niese's first regular-season assignment will come in the second series, against the Atlanta Braves at Turner Field.