Eddie Butler escaped several jams to throw 5 1/3 scoreless innings, combining with five Colorado relievers on a five-hitter as the Rockies posted a 2-0 win in the Giants' home opener.
Butler (1-0) worked around six walks and five hits allowed by continuing San Francisco's recent struggles in clutch situations, with the Giants stranding a total of 12 runners en route to a fourth straight loss.
San Francisco went 0-of-7 with runners in scoring position and is hitting an anemic .091 (3-of-33) in such situations during its skid.
Heston (1-1) pitched well for a second straight start in place of an injured Matt Cain, with the rookie yielding two runs -- one earned -- and striking out five over seven innings in a hard-luck outcome.
Nori Aoki finished 2-for-4 for San Francisco to extend his hitting streak to 16 games.
Despite landing in trouble for a large portion of his effectively wild outing, Butler was able to keep the Giants off the board by preventing the big hit.
The young righty worked out of bases-loaded jams in each of the first two innings and stranded two more runners in the third. San Francisco threatened again an inning later, with a single by Aoki and a walk to Joe Panik putting two on with one out. But Butler induced a double-play grounder to Angel Pagan to end the fourth, two of the 11 outs he recorded on the ground on the afternoon.
Heston, meanwhile, faced the minimum before Charlie Blackmon singled to lead off the fourth and took second on a groundout. The rookie then hung a curveball that Tulowitzki hammered to left for a single that brought in the game's first run.
Hundley doubled off Heston and scored an insurance run in the seventh. After advancing a base on DJ LeMahieu's infield hit, the Colorado catcher was able to dislodge the ball from Heston's glove while rumbling home on a pitch in the dirt.
The Rockies' bullpen didn't permit a hit over a combined 3 2/3 innings of work, with Rafael Betancourt fanning two in a perfect ninth to save Butler's second career win as a major leaguer.
Betancourt was given first crack at replacing LaTroy Hawkins, removed from the closer's role by manager Walt Weiss after giving up three runs in the top of the ninth of Sunday's 6-5 loss to the Cubs.
The Giants lost for only the third time in their last 15 home openers ... Hesston became just the second rookie pitcher to start a Giants home opener. Alan Fowlkes got the nod against San Diego at Candlestick Park in 1982 ... LeMahieu went 3-for-4 and is batting .517 (15-of-28) during a seven-game hitting streak to begin the season ... San Francisco third baseman Casey McGehee missed a second straight game due to a bone bruise in his left knee ... The Giants are 0-for-6 in bases-loaded situations so far this season