SAN FRANCISCO -- Rockies right-hander Adam Ottavino has emerged as an intriguing possibility as a "piggy-back pitcher" in the team's paired pitching rotation -- four starters, plus three relievers who can pick up when starters reach closely monitored guidelines for when they should be removed.

Righty Josh Roenicke (4-0, 2.21 ERA) has been the club's most effective piggy-back, but Ottavino (3-1, 4.34 ERA) has shown steady improvement. Ottavino's contribution was major in Friday night's 3-0 victory over the Giants. He threw two hitless innings and escaped a one-out, two-on jam in the seventh. Ottavino had walked two hitters -- he credited the hitters' patience -- but escaped the inning unscathed.

To move forward, Ottavino, 26, will have to continue making adjustments at home and on the road. His best pitch, his slider, can be nasty on the road, but it's tougher to achieve that action in the altitude at home. Still, he has been competitive both places -- 2-0, 4.82 ERA in 27 appearances at Coors Field, and 1-1, 3.80 ERA in 10 games on the road.

"At home, it's a little harder to get [the slider] to break the way you want it to. But I've found that if you stay on top of it, you can still make it do good things in terms of depth," Ottavino said. "On the road, it just happens a little more regularly.

"I like to throw my breaking ball sometimes with more depth, sometimes more downward, sometimes I mix both -- so it's really three different pitches in one. It's a little easier to do on the road."

Back keeps Fowler out on Saturday

SAN FRANCISCO -- Rockies center fielder Dexter Fowler felt his back spasm when reaching for a fly ball early in Friday night's 3-0 victory over the Giants, and sat out Saturday's 9-3 loss to the Giants.

The injury was nowhere serious enough for the Rockies to place Fowler (.290, 12 HR, 41 RBIs) on the 15-day disabled list. Manager Jim Tracy said prior to the game he would try not to use Fowler in a reserve role on Saturday, then would re-evaluate him on Sunday.

"I don't have a clue [how long it will be before I can start again]. It just came up on me, so you never know," Fowler said. "I reached up and felt it in my back. It was my whole back, so it wasn't just one spot. I think it was a spasm."

Eric Young Jr. started in center and recent callup Matt McBride made his first career Major League start in right -- a difficult place at AT&T Park, with its odd dimensions and strange bounces off the wall. McBride, who joined the Rockies in the Ubaldo Jimenez trade with the Indians last year, has played catcher, outfield and first base in the Minors.

"This is a nice right field to learn how to play in," Tracy said. "It's an opportunity to see both from [McBride] -- play him at first base, play him some in the outfield. That's exactly what he was doing in the Minor Leagues. I like to see people for myself, so I don't have to rely on so many other opinions."

Escalona placed on 15-day disabled list

SAN FRANCISCO -- The Rockies placed right-hander Edgmer Escalona on the 15-day disabled list with right triceps tendon inflammation. They purchased the contract of righty reliever Will Harris, who went a combined 4-1 with a 2.09 ERA in 44 games with Double-A Tulsa and Triple-A Colorado Springs.

Harris, 27, struck out three in 1 2/3 innings for Colorado Springs on Friday and wasn't expected to land in San Francisco until gametime on Saturday, so it was unlikely that he would be used. After piling up 66 strikeouts to 13 walks in 66 games, including 20 strikeouts and one walk at Triple-A, the former LSU pitcher has a chance to show Rockies manager Jim Tracy what he can do.

"What I hear about him is so encouraging. ... He has pounded the strike zone with a lot of energy -- he will not back off," Tracy said. "I was very intrigued when I heard about the command and the way he has aggressively attacked the strike zone. I like to hear about stuff like that. The opportunity is here for us to find out a little bit more information."

Worth noting

• Righty Tyler Chatwood (2-2, 5.06 ERA) earned another start -- which will be his third since being called up from Triple-A Colorado Springs -- with his five scoreless innings in Friday night's 3-0 victory over the Dodgers. Chatwood has been penciled in for Tuesday's game at home against the Brewers.