HOUSTON -- Nationals slugger Alfonso Soriano has made significant strides in left field since Spring Training. Thanks to the coaching he has received from first-base coach Davey Lopes and Jose Cardenal, the special advisor to the general manager, Soriano is catching routine fly balls, line drives to his left and right and balls over his head.

However, he needs to improve his throwing in the outfield. With Craig Biggio on third base in the bottom of the third inning of Friday's game, Astros outfielder Lance Berkman hit a fly ball to Soriano, who caught the ball and sidearmed it to third baseman Ryan Zimmerman, who then threw home, but Biggio beat Zimmerman's throw home.

Soriano acknowledged that he needs to throw overhand in order for the ball to reach home plate.

"I need to change it. I throw like an infielder. I don't know how to throw like an outfielder," said Sorinao, who has played most of his Major League career as a second baseman.

Lopes said it will take time, maybe the entire season, for Soriano to get used to throwing overhanded.

"It's going to take a lot of time and work to throw like an outfielder. His natural instinct is to catch it and play that ball with the arm slot that he is accustomed to. If that's the least of our problems, I'll take that," Lopes said. "You can't expect everything to be so polished at the early stages, but he doing a good job catching the ball and he has made adjustment coming in on balls. It's a work in progress, but he's doing a good job.

Lopes knows what it is like to change a throwing technique. He was an outfielder when he started his professional baseball career with the Dodgers. He then had to learn to throw sidearm when Los Angles made him a second baseman. Lopes turned out to be a good one for over a decade.

"I was fortunate that I had an Instructional League to eliminate [the habit of throwing overhand], and it took time. Soriano doesn't have that time," Lopes said. "I would venture to say that it's not going to happen this year, because he doesn't have enough time to practice. Once the game starts, you just rear back to your normal instincts. That's what he's doing right now."

More on Soriano: With the Nationals leading, 9-6, in the seventh inning on Saturday, manager Frank Robinson took Soriano out of the game against the Astros for defensive purposes. Soriano, who is known to play almost every inning of every game, went to Robinson after the game and wanted to know if he did anything wrong. Robinson said, "No," and told Soriano that he was doing a good job in the outfield.

"But I said I had a better defensive player sitting on the bench [in Damian Jackson], and I wanted him to play defense with a three-run lead," Robinson said. "He said, 'OK, but I like to play all the time.' "

Doing the job: If Marlon Byrd continues to be consistent with the bat, Robinson is prepared to play him on a more regular basis, which would mean less playing time for Brandon Watson.

"If somebody is hot, you reward him if the other guy is struggling a little bit. That's the nature of the game," Robinson said. "As a manager, you have to take advantage of the guys when they are swinging the bat well."

Byrd is currently the fourth outfielder, but he started Sunday's game because Watson is in a 3-for-19 slump. Byrd responded by opening the game with a home run to left.

Byrd also is expected to start on Monday against the Astros.

Injury report: On Saturday, Jose Guillen, who was playing with a sore left forearm, entered the game as a pinch-hitter in the seventh inning, went 2-for-2 and played a big part in the six-run rally. Since joining the Nationals, Guillen has been known to come back from an injury and deliver in the clutch. His most famous game came against the Giants on May 7, 2005. A day after suffering a contusion on his left triceps, Guillen entered the game in the fourth inning and delivered a two-run single against Jason Schmidt. He ended up going 2-for-4 in an 11-8 victory.

"He is amazing. You just don't count him out. He wants to play and he came in [on Saturday] and he surprised the heck out of me," Robinson said. "He walked into the office with a bat in his hands and I said, 'Where are you going?' He said, 'To the batting cage.' He said, 'I know you gave me the night off, but I'm ready to pinch-hit.' "

Guillen started Sunday's game against the Astros and is wearing a protective shield on the forearm.

No surprise: Following Saturday's 12-8 win, the Nationals optioned reliever Jason Bergmann to Triple-A New Orleans. The news comes after he was unable to retire a batter on Friday against the Astros. He gave up four runs in the game.

The next day, the Nationals activated Ryan Drese, who started Sunday's game against the Astros.

Stat of the day: Entering Sunday's action, Nationals batters have been hit by pitches eight times, which leads the Major Leagues. The Blue Jays rank second with six.

Did you know? Entering Sunday's action, Jose Vidro has homered in consecutive games. The last time he did that was in Aug. 21-22, 2002, against the Rockies.

Coming up: The Nationals return to Minute Maid Park on Monday afternoon to play the Astros at 2:05 p.m. ET.

Right-hander John Patterson will get the start for Washington, while left-hander Wandy Rodriguez gets the nod for Houston.

Patterson got off to a slow start, giving up four runs to the Mets on Wednesday. It didn't help that he was playing with a forearm injury. He hopes to redeem himself on Monday as he faces the Astros for the third time in his career. He is 1-0 with a 2.63 ERA against them.