SCOTTSDALE, Ariz. -- A player's true defensive prowess is difficult to summarize in statistics, although some people try -- including John Dewan, author of "The Fielding Bible."

And, according to Dewan's ratings, Dave Roberts led all Major League left fielders in Plus/Minus ratio, recording a plus-16 with the San Diego Padres. This reflects the number of plays a player makes above (or below) those an average performer at his position would make.

This suggests that Roberts, 34, should be able to handle the transition back to center field for the Giants. He moved to left last season after the Padres acquired Mike Cameron.

"It's not all about just making the highlight plays," Roberts said Friday, discussing his defensive approach. "It's all about making the right plays, the plays you're supposed to make and throwing to the right base."

Conventional evidence speaks well for Roberts, too. He was the Majors' only qualifying left fielder (minimum 108 games) not charged with an error last season. Anecdotal evidence? In 2003 with the Dodgers, he became the first player to ascend "Tal's Hill" -- the unusual incline in center field at Houston's Minute Maid Park -- to make a catch.

"Defense is a big part of winning baseball," Roberts said. "People don't realize that it helps your pitching staff -- not only with sheer ERA or runs scored, but in the number of pitches they have to throw. In turn, it saves the bullpen. Over the course of a 162-game season, not getting the outs you're supposed to get adds up."

What a beating: Manager Bruce Bochy resorted to sarcasm to summarize the Giants' 21-2 exhibition loss Friday to a Milwaukee Brewers split squad.

When a reporter mentioned that the Giants' legion of flu-stricken players was dwindling, Bochy said, "It certainly looks like we all had it today."

The Brewers, who finished with 24 hits, amassed 10 runs and 10 hits before the Giants recorded a single out in the third inning. Left-hander Steve Kline was San Francisco's only pitcher to work a full scoreless inning as Milwaukee scored two or more runs in six different innings.

"We got the ball up a lot," Bochy said. He noted that the Brewers collected "eight or nine" broken-bat hits but didn't mean to discredit them. "They found holes everywhere out there," Bochy added.

Left fielder Barry Bonds went 0-for-2 in his first spring appearance, grounding out and striking out, but reported no problems with his troublesome right knee.

"It's great that his knee feels good and that he's excited about it," Bochy said.

Cain's unruffled: Matt Cain knew better than to let the results of his two-inning stint against Milwaukee bother him.

Cain allowed five runs in the second inning, but the Brewers' surge began when Bonds dropped Mike Rivera's wind-blown fly ball. It was scored a double, putting runners on second and third with one out. Cain coaxed a popup from Drew Anderson before JD Closser dumped a two-run single in front of Bonds. Cain walked opposing pitcher Carlos Villanueva -- his worst mistake -- before the gusts carried Hernan Iribarren's fly ball over the right-field wall for a three-run homer.

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"It's a tough day out there," Cain said. "The wind and sun didn't help us too much. Look at the flags -- they looked like they soaked them in starch. They were standing straight up."

Of Iribarren's homer, Cain said, "I'm not trying to take anything away from him, but when he hit it, I didn't think it was [a home run]."

Said Bochy, "The numbers weren't indicative of how he threw. The home run was a fly ball. That's why it's so tough to read games here."

Feeling better: Four players stayed at home with the flu, down from Thursday's eight. Those who remained too ill to work out were pitchers Armando Benitez, Tim Lincecum and Osiris Matos and catcher Todd Jennings.

If Lincecum stays sick Saturday, his scheduled start in Monday's "B" game against Oakland could be in doubt.

First baseman Rich Aurilia and right fielder Randy Winn, among those sidelined by the flu Thursday, returned to participate in pregame drills. Aurilia reported that he had endured a 103-degree fever. Both he and Winn are expected to start Saturday against Milwaukee.

Signees: The Giants agreed to terms on one-year contracts with 23 players: pitchers Kelyn Acosta, Vinnie Chulk, Kevin Correia, Brad Hennessey, Matos, Pat Misch, Scott Munter, Billy Sadler, Jonathan Sanchez, Jack Taschner, Erick Threets, Merkin Valdez and Brian Wilson; outfielders Jason Ellison, Fred Lewis, Todd Linden, Dan Ortmeier and Nate Schierholtz; infielders Kevin Frandsen, Travis Ishikawa, Lance Niekro and Eugenio Velez; and catcher Eliezer Alfonzo.

Coming up: The Giants have a rematch with Milwaukee on Saturday at Maryvale Baseball Park. Right-hander Matt Morris will start against Milwaukee counterpart Ben Sheets.