CHICAGO -- A day before he was scheduled to pitch, Nationals left-hander Odalis Perez had a talk with manager Manny Acta. The gist of the conversation was that Acta wanted Perez to ignore Angel Hernandez, who was scheduled to be the first-base umpire on Saturday at Wrigley Field.

Why did this conversation take place? On July 8 at Nationals Park, Perez was ejected from the game against the Diamondbacks in the third inning after arguing a balk call with Hernandez, who was the home-plate umpire. The balk was the second called on Perez in the inning. He would be later fined for the incident.

"We already spoke about that, and the game is bigger than Odalis and Angel Hernandez," Acta said. "We are just going to play our game. Odalis is not going to go out there thinking about whatever might happen. He is just going to try to get hitters out."

Hernandez had no effect on Perez on Saturday, but the left-hander ended up having one of his worst outings, as the Nationals were defeated by the Cubs, 9-2, at Wrigley Field.

Perez lasted 4 1/3 innings and gave up five runs (four earned) on 10 hits. It didn't help that Perez was suffering from a stomach virus before the game. He believes chicken noodle soup did him in.

It's not the first time Perez felt weak before a game. On May 28, Perez went to a dentist in San Diego and ended up in the dentist's chair for more than four hours while getting a root canal. When he arrived at PETCO Park, Perez felt weak because of the medication he was given by the dentist, but he never thought about missing his turn. He knew before the game he couldn't overpower the Padres, but he somehow found a way to keep them off balance and help the Nationals win the game.

On Saturday, Perez arrived at the ballpark early and ate the soup around 11:40 a.m. ET. He then felt bad after finishing the meal, but he took some medicine that made him strong enough to make the start.

Although he felt well enough to pitch, Perez still didn't feel quite right on the mound. It was obvious from the first inning that Perez had nothing in the tank. The Cubs had at least two runners on base during each of the first three innings without scoring.

However, Chicago would get to Perez in the fourth. After Alfonso Soriano started the inning with a walk and Ryan Theriot followed with a single, Derrek Lee singled to left-center field to send Soriano home. Aramis Ramirez followed by drilling a 1-2 pitch over the left-center-field wall for a three-run homer that gave the Cubs a 4-0 lead.

After the game, Perez said Hernandez never entered his mind while he was on the mound. He simply had a poor start because he didn't feel well.

"I didn't think I had my best stuff," Perez said. "When I got to the ballpark, I started feeling weird in my stomach. ... Obviously, that's not an excuse. I wanted to go out and do well, but I didn't have it today.

"Whatever happened between Angel and me is in the past. I had no concerns that he was at first base. I wasn't afraid to throw over there, nothing like that."

After giving up an RBI double to Soriano in the fifth, Perez left the game with a cut on his left thumb. It was the nail of his index finger that cut the thumb while he was making a pitch in the fourth inning. Perez believes he will be able to make his next start against the Braves on Friday at Nationals Park.

"I cut myself a little bit, but I don't think it's a big deal," Perez said.

After erupting for 13 runs in the series opener, the Nationals went back to their old ways with the bats. They had no answers for Cubs starter Ryan Dempster, who gave up one run in 7 1/3 innings.

The Nationals had a chance to put Dempster behind early, when they had runners on first and second and one out in the first, but Lastings Milledge hit into a double play to end the inning.

Their lone run off Dempster came in the top of the seventh inning, when Austin Kearns scored on a single by Anderson Hernandez.

"He's tough," Acta said of Dempster. "He has a good repertoire. His offspeed stuff is so good. When he has command of it, he throws a lot of them. Check around in the big leagues -- more than 90 percent of them are not good offspeed hitters."

Dempster's offspeed stuff wasn't the only thing that bothered the Nationals' hitters.

"He came inside and he wasn't scared," Milledge said. "It was a bright day today. Everything is pretty much working against you."