PHOENIX, Ariz. -- When Chris Heston took the mound for his first bullpen session this spring, he looked down to the plate and saw Buster Posey waiting to catch him. General manager Brian Sabean stood behind a chain-link fence and manager Bruce Bochy and pitching coach Dave Righetti planted themselves alongside the right-hander, watching closely.

"You try to block stuff out, but it was impossible not to notice that," Heston said afterward. "That guy down there that's catching you is the MVP."

Posey wasn't on hand during a "B" game at the Arizona Diamondbacks facility Sunday, but Heston and fellow prospect Mike Kickham again drew an influential crowd, despite the early start time. Bochy and Righetti were on the bench for the game, and Sabean watched with a handful of his lieutenants.

The implication was clear: Heston and Kickham will be counted on, possibly sooner rather than later.

"You need depth in your rotation, and these are two guys we think a lot of," Bochy said. "If needed at some point, they'll be ready. Both of them, I thought, did a real nice job."

Heston threw three innings against Diamondbacks minor leaguers, giving up just two hits and striking out four. Kickham struck out the side in his first inning before giving up a run on a sacrifice fly in his second frame.

Heston, a strike-throwing righty, and Kickham, a left-hander with electric stuff, couldn't be more different on the mound. But they're practically inseparable off it.

"It's not a rivalry," Kickham said. "But I do always try to keep up with him. We're two very different types, but you can emulate success."

There was plenty of that last season at Double-A Richmond. The 24-year-old prospects were twin terrors for the rest of the Eastern League. Heston had a 2.24 ERA and was the league's pitcher of the year, while Kickham joined his friend on the league's All-Star team after going 11-10 with a 3.05 ERA and a team-high 137 strikeouts in 1502/3 innings.

Heston has a clean, repeatable delivery and relies on a variety of pitches, including a sinker that he learned from former Giants left-hander Steve Kline two seasons ago. Posey was impressed when he caught Heston, saying he "clearly has a very good idea of what he wants to do with every pitch."

Heston has caught Matt Cain's eye, too.

"He's real easy" with his delivery, Cain said. "He looks pretty smooth."

Heston was pleased with Sunday's outing because he was able to keep the ball down and let the defense go to work. He got four ground-ball outs in his three innings of work, and one of the two hits was an infield single. The outing was a far cry from his previous two appearances, when Heston gave up five earned runs on eight hits in just 22/3 combined innings.

"I was happy for Chris," Bochy said. "That had to do a lot for his confidence."

Kickham had given up just two hits over three innings in two previous innings this spring, and he again looked sharp Sunday. The left-hander sat between 91 and 93 mph with his fastball and flashed a devastating but inconsistent curveball.

"He's just nasty," Heston said. "His stuff is some of the best I've seen. When he dials it in, he's almost unhittable."

Heston says the two have a "healthy competition" and try to one-up one another. The competition will likely take place at Triple-A Fresno this season, where the Giants have few young pitching prospects. The system's depth is at the lower levels, with the likes of Kyle Crick, Clayton Blackburn and Chris Stratton viewed as future big league contributors.

But the Giants know that they've been remarkably lucky with starting pitching health in recent years, and they'll likely need a boost at some point. Heston or Kickham, or both, could be the ones to provide it.

"This is probably the first time these eyes are seeing you at length," Heston said. "We're trying to take advantage of every opportunity to showcase our talent."

  • Cain gave up four hits and a run in a 6-1 victory over the Milwaukee Brewers but left after the third inning because of an upset stomach. "Something at dinner didn't agree with me," Cain said.

    Cole Gillespie and Wilson Valdez had two hits apiece for the Giants, who snapped a four-game Cactus League losing streak.

  • Bochy and Cain both said they watched Ryan Vogelsong pick up the victory with four-plus strong innings for Team USA on Saturday night.

    "He threw the ball really well," Cain said. "That's typical Vogey. That's pretty awesome for him to get the win. I know he's pumped up about it."

    Cain had just one issue with Vogelsong's performance.

    "It's not fair," he said, laughing. "I wish we could get a win after four innings."

  • Bochy wasn't sure when players who were from eliminated WBC teams would return to camp, but Sergio Romo could be back as soon as Monday. Pablo Sandoval and Marco Scutaro also are expected back in camp soon.

  • Tony Abreu will make his spring debut Monday after missing several weeks with a strained quad. Abreu is still viewed as a strong candidate to win the final roster spot in the infield.

    For more on the Giants, see Alex Pavlovic's Giants Extra blog at blogs.mercurynews.com/Giants. Follow him on Twitter at twitter.com/AlexPavlovic.