FRANCISCO (AP) -- Russ Ortiz was an aspiring closer. Joe Nathan played shortstop most of his life. Both have pulled off pitching transitions for the San Francisco Giants with startling results. Ortiz, just two years removed from being considered the top relieving prospect in San Francisco's farm system, has emerged as a top-flight starter. And Nathan, pitching above Double A for the first time this season, already has made an overpowering impression in the rotation and the bullpen with his 97 mph fastball. The two have been central to San Francisco's solid start, figuring in eight of the team's 23 wins. Their success also has helped San Francisco withstand an injury to opening day starter Mark Gardner and the ongoing struggles of Shawn Estes. The Giants, who have played the past month without Barry Bonds, began Thursday tied with Arizona for first place in the NL West. ``I look at them as young pitchers but they're pitching like they've been around a long time,'' outfielder Stan Javier said. Ortiz has gone 5-2 with a 2.53 ERA, both ranking near the top of the league. He has won his last four decisions, a career best, and the Giants have wins in 11 of his last 14 outings. ``It's fun for me to see younger guys do well and prove they can play up here,'' said Ortiz, who has his first career complete game in a 7-2 win over Colorado on April 23. ``I'm just throwing better pitches and getting my breaking pitches over for strikes. Last year, I would throw the fastball and not even worry about location.'' Pitching coach Ron Perranoski said Ortiz used to throw a fastball almost exclusively, which was one of the main reasons he mostly worked out of the bullpen in the minor leagues and in college at Oklahoma. Ortiz split time between the bullpen and rotation and between San Francisco and Triple-A Fresno last season but settled into a starting role after filling in for the injured Estes much of last season. His ability to diversify his pitching style accelerated his transition from reliever to starter. ``But I think the biggest factor in his last 5-6 starts is when he makes a pitch, he's not overthrowing,'' Perranoski said. ``Right now, he's got the hot hand and he's our most consistent pitcher.'' Nathan, though, rates as an even bigger surprise for the Giants than Ortiz. He began as an infielder in San Francisco's minor league system but Giants scouts were dubious about his hitting prospects and intrigued by his powerful throwing arm and suggested he switch to pitching. ``He was a tall skinny kid at shortstop but he had a great arm,'' Perranoski said. ``We thought he could be a pitcher and as it turned out we were right.'' Nathan agrees now but he wasn't sold on the idea at first, leaving the organization and returning to State University of New York-Stony Brook for a year to complete his degree. Deciding to give baseball one more shot, he rejoined the Giants in 1997 and rose to become one of the Giants top pitching prospects, nearly making the team out of spring training prior to this season. The Giants recalled Nathan after shoulder problems forced Gardner on the disabled list and Nathan responded by pitching seven scoreless against Florida on April 21 to win his major league debut. ``I don't want to think too much about what's happened because I don't want to change anything in what I've done to get where I am,'' Nathan said. ``Basically, I've just tried to keep things simple.'' He won his next start against Montreal by allowing two runs in eight innings, becoming the first Giants pitcher since Osvaldo Fernandez in 1996 to win his first two starts. He just missed becoming the first San Francisco pitcher since Juan Marichal in 1960 to win his first three starts, leaving a May 3 contest at Pittsburgh with a 6-4 lead but the Pirates rallied for a 9-8 decision. Earlier this month, he moved to the bullpen as Gardner returned from the disabled list to reclaim his starting spot and setup man Julian Tavarez, suffering from pneumonia, went on the disabled list. Last Sunday at Houston, Nathan worked a scoreless 11th inning, fanning Jeff Bagwell for the final out, to pick up his first major league save. ``It was great because he had never been in that situation before at any level and it was a big game for us,'' Javier said. ``When you have a 97 mph fastball and you throw it past Bagwell, that's something.'' -=-=- 