SAN FRANCISCO -- The irony of George Kontos' yeoman relief stint Monday night was impossible to miss. For delivering extra effort and rescuing the Giants' bullpen from overuse, he was demoted.

Kontos threw 3 1/3 innings and 63 pitches, both career highs, in the Giants' 11-0 loss Monday to Cincinnati. That prevented the Giants from depleting their bullpen after Tim Lincecum's 3 2/3-inning performance. But it left Kontos unable to pitch for two or three days, which included Tuesday's doubleheader against the Reds. So the Giants, needing a fresh pitcher capable of providing long relief, purchased the contract of Yusmeiro Petit from Triple-A Fresno.

Meanwhile, Kontos was optioned to Fresno.

"They made the most logical move, I guess," said Kontos, who nevertheless appeared sullen as he sat by his AT&T Park dressing stall.

Kontos said that manager Bruce Bochy "seemed almost apologetic" while informing him of the move. With reporters, Bochy was logical. He noted that Kontos would have to rest his arm for the next few days and added, "We felt we needed somebody who can help us for two or three innings so we don't overuse anybody. That's why the move was made."

Kontos was 2-2 with a 5.05 ERA in 42 appearances, which was tied for the club lead with Javier Lopez entering Tuesday.

"We look at George as a guy who will be back up," Bochy said.

Petit had stints with the Marlins (2006) and Diamondbacks (2007-09) before replacing Tim Lincecum for one start last Sept. 23 -- one day after the Giants clinched the National League West. With Fresno, Petit was 5-4 with a 5.24 ERA in 12 starts, including a 3-0 mark and 2.57 ERA in his last three outings.

To clear room for Petit on the 40-man roster, the Giants designated Minor League right-hander Hunter Strickland for assignment.

Arias begins rehab assignment on Wednesday

SF@LAD: Arias strains hamstring, forced to leave game

SAN FRANCISCO -- Giants infielder Joaquin Arias, who underwent an appendectomy on July 8, will begin his rehab assignment with Triple-A Fresno on Wednesday.

Arias is hitting .282 with a .302 on-base percentage and 10 RBIs in 110 at-bats this season.

During Arias' time away from the club, Tony Abreu has seen his role expand with playing time at shortstop and second base.

Although there is no set timetable for players to return from an appendectomy, it typically takes two or three weeks. Arias will begin his rehab assignment two weeks and two days following his surgery.

Heston clears waivers, becomes free agent

SAN FRANCISCO -- Minor League pitcher Chris Heston cleared waivers and was released by the Giants on Tuesday. He is now a free agent.

Heston was designated for assignment July 13 when the club signed outfielder Jeff Francoeur and needed to free up a spot on the 40-man roster.

He impressed in 2012 when he posted a 2.24 ERA in 148 2/3 innings in 2012 at Double-A Richmond. While he is not a hard thrower, his bread and butter was inducing groundouts.

This year, at Triple-A Fresno, he struggled with a 5.80 ERA in 108 2/3 innings. San Francisco had protected him from the Rule 5 Draft last offseason by placing him on the 40-man roster.

Giants not considering using Belt in left field

SF@SD: Belt drives a two-run homer to right-center

SAN FRANCISCO -- Collectively, Giants left fielders have been underperforming dramatically on offense. Yet manager Bruce Bochy politely nixed the suggestion of using Brandon Belt in left field to keep his bat in the lineup.

"We haven't been thinking of putting him in left," Bochy said Tuesday.

Belt, San Francisco's primary first baseman, typically sits on the bench when catcher Buster Posey makes his occasional starts at first, as was the case in the first game of Tuesday's doubleheader against Cincinnati.

But the numbers don't lie. Belt, who has started 35 games in left field during his three Major League seasons, has outperformed the Giants' left-field contingent in virtually every significant offensive category.

San Francisco's left fielders entered Tuesday ranked last among their National League counterparts in runs scored (38) and home runs (two), next-to-last in OPS (on-base plus slugging percentage, .678) and 11th in RBIs (34). The league averages in those categories, respectively, were 53, 13, .759 and 44. Giants left fielders were a respectable seventh in batting average (.272), exceeding the league average of .263.

Belt's statistics entering Tuesday suggested that he might be able to improve upon the team's left-field production, even if he plays there only occasionally. He ranked second on the club in runs (42) and OPS (.788), third in homers (10), fourth in RBIs (38) and fifth among qualifying players in batting average (.268).