PITTSBURGH - Oliver Perez came out of spring training a year ago as a very shaky No. 5 in the Pittsburgh Pirates' rotation, a 6-foot-2 bundle of unpolished but undeniable talent.

After arguably the best debut season by a Pirates left-hander in 30 seasons, Perez goes into Monday's opening day start against Milwaukee as their clear-cut No. 1 starter and one of the majors' on-the-rise stars.

Perez will go against another of baseball's best young starters in Ben Sheets - a matchup that likely would be attracting more attention if their teams weren't so bad. Between them, Sheets and Perez struck out 503 with a 2.83 ERA last season, yet were only a combined 24-24 - partly because the Brewers scored only 19 runs in Sheets' 14 losses.

Perez is not yet a finished product, but is much closer to being one than a year ago, when he spent an unsettled spring training smoothing out an erratic, herky-jerky delivery that might have left him susceptible to arm injuries if it had gone uncorrected.

Now, with a heavy fastball that sometimes makes hitters wish they didn't make contact and two different knee-buckling sliders, the Pirates think they've got their staff ace for years to come, barring injury. No young Pirates starter made such an impact in his first season since one-time 20-game winner John Candelaria, who helped them reach the NL playoffs as a rookie in 1975.

That's why manager Lloyd McClendon can't wait to hand Perez the ball on Monday - and, he hopes, do so for many more opening days to come.

"The sky's the limit for him," McClendon said. "We think we've got something special. I don't think he's a player who is motivated by dollars, he's motivated by competition. He wants to be the best."

Perez doesn't turn 24 until August, yet he gave a glimpse of what he could be with a 12-10 record, 2.98 ERA, 239 strikeouts and a 2.21 home ERA last year. His average of 10.97 strikeouts per nine innings was the majors' best, topping even Randy Johnson - prompting the Braves' Chipper Jones to predict Perez will be the NL's new Big Unit, now that Johnson is with the Yankees.

"This is where you want to be," Perez said of his first opening-day start. "This is what everybody wants to do."

Sheets, 26, feels much the same way about his fourth consecutive opening day start following an effective but often excruciating 2004 season that saw him go 12-14 despite a 2.70 ERA.

"It means a lot," Sheets said. "It means you did something right the year before. It's an honor."

The right-hander was so bothered by a herniated disc in his lower back that he sometimes couldn't bend over to pick up the ball. He got through the season only through stretching exercises and anti-inflammatory medication before having back surgery Oct. 12, yet could have easily been an 18-game winner with marginal run support.

Neither the Brewers (67-94) nor the Pirates (72-89) did much right while losing a combined 183 games last season - the 12th consecutive losing season for both, four shy of the major league record.

The Pirates did little tinkering during the offseason, subtracting catcher Jason Kendall and adding right fielder Matt Lawton and left-handed starter Mark Redman. The Brewers' major addition is Carlos Lee, who hit .305 with 31 homers and 99 RBIs for the White Sox.

Manager Ned Yost's major concern is a rebuilt bullpen that doesn't look as strong without closer Dan Kolb (39 saves), dealt to Atlanta for pitching prospect Jose Capellan, or setup man Luis Vizcaino. For now, Mike Adams, who does not have a save, is the closer.

Despite an early spring storm that pelted PNC Park with snow and 45-mph wind gusts Sunday, Monday's forecast is much better, with a high of 60 under partly sunny skies.