He'll be taking what once was scheduled to be the turn of No. 4 starter Joe Blanton, who was officially moved into the No. 2 spot Sunday when the A's placed righty Esteban Loaiza on the 15-day disabled list with a strained right trapezius.
"It's not like I've never done it before," he said. "I've done it most of my life."
Of Gaudin's 87 career appearances in the Minors, 68 came as a starter, and last season he went 3-0 with a 0.37 ERA in four starts at Triple-A Sacramento before being called up to Oakland for good in May.
He made two starts this spring, including a 66-pitch outing Saturday at AT&T Park against the Giants, and will be on an 80-pitch limit against the Halos.
"If we need him to make a second start, he'll be stretched out enough by then to slide right into that No. 4 spot for as long as we need him," A's manager Bob Geren said. "Hopefully it won't come to that."
The hope is that Loaiza, who has been experiencing spasms under his right shoulder blade for the past several days, will be able to start for Sacramento on Thursday and return to the A's rotation April 10 against the White Sox.
"There's still some tightness and soreness, but it feels better," Loaiza said before Sunday's game. "I'd rather miss one or two starts instead of trying to go out and pitch [through it] and risk missing 30 starts. It's better to just take care of it now."
Red-hot redhead: Outfielder Bobby Kielty, who underwent minor knee surgery in early March, went 3-for-3 with a double against the visiting Giants on Sunday to raise his batting average to .500 (7-for-15) in five games since his return to action.
Though Geren said Travis Buck and Shannon Stewart will be his primary corner outfielders, he added that Kielty "will get a lot of at-bats."
"I'm going to be cautious with everybody," Geren continued, "so there will be plenty of playing time to go around. And Bobby's a heck of a hitter, particularly from the right side, so we have to get him in there as much as we can against lefties."
Geren said Kielty likely will start in right field Tuesday, when the Mariners are scheduled to start lefty Jarrod Washburn.
Good news, bad news: Veteran infielder Lou Merloni, who drilled an RBI double into the left-center gap to spark a five-run rally in the sixth inning Sunday, said he feared being released when he was called into Geren's office.
So he was strangely relieved to be told that he'd been reassigned to the Minor League camp.
"It's been this way for me for nine years; I've never gone into camp with a job," he said. "But I've made it to the Majors for a least a little while every year, so hopefully I can keep the streak alive. I'm just glad I still have a job, even if it's at Triple-A. ... This is a tough time to be looking for work."
Recently signed Todd Walker was given one of the utility jobs Merloni had hoped to land, and like Walker, Merloni can play all over the infield. He batted .289 while platooning at first base with Ben Broussard for the Indians in 2004, and he played third base most of the time this spring.
"He's right there," Geren said of Merloni. "I was in the Red Sox organization when he signed there [in 1993], so I've seen him play a long time, and I have a lot of confidence in him. He's a very good all-around baseball player."
Dribblers: No. 5 starter Joe Kennedy gave up four runs on five hits over six innings Sunday, with three of the runs coming on two homers by Barry Bonds. "He got a couple of ball up to Bonds, but other than that, I thought he was very effective," Geren said. ... Of Bonds' seven spring homers, three came at the expense of the A's. ... Bradley played one inning, grounding out in the bottom of the first before leaving the game. "That's all he wanted, one at-bat," Geren said. Bradley reached base safely in 16 of the 18 spring games in which he played. ... Former A's ace Barry Zito, who signed with the Giants as a free agent in the offseason, called his first appearance at McAfee Coliseum in black and orange "surreal." A common taunt thrown at Zito on Sunday was "Nice shoes!" ... Longtime A's public-address announcer Roy Steele, who was ill for much of 2006, was back behind the microphone Sunday and is expected to resume full-time duties during the regular season.
Up next: Righty Dan Haren will make the first Opening Day start of his career Monday afternoon opposite 20-year-old Felix Hernandez of the host Mariners at 3:35 p.m. PT Game-time temperatures are expected to be in the high 40s, with a 30 percent chance of rain, so the roof at Safeco Field will be closed.
Mychael Urban is a national writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.