Hoffman (2-0) also had his first big league hit and the National League-leading Rockies continued to cruise away from home. They are the best in the majors with a 16-7 road record and are 5-2 on this season-long 10-game road trip.
The 22-year-old-Hoffman, rated Colorado's No. 2 prospect, made his second spot start of the season. He was needed because the Rockies played a doubleheader last week and went with Hoffman rather than use a starter on short rest. He'll likely return to the minors but certainly impressed against the woeful Phillies.
The tarp covered the field until 30 minutes or so before first pitch, the sixth straight game the Rockies failed to take batting practice.
Hoffman, the No. 9 overall pick in the 2014 draft, threw 99 pitches and flashed the command needed to establish himself as a future member of the rotation. He retired the first 11 batters of the game and struck out Maikel Franco with runners on first and third to end the fourth.
"He has the physical attributes to be a good one," manager Bud Black said. "There are some other boxes he has to check off."
Hoffman checked a box or two against the Phillies.
But a lot of pitchers are sharp this season against the struggling Phillies. Philadelphia opened a seven-game homestand with its 18th loss in the past 22 games.
"There's more talent on this team than what we've shown," Phillies general manager Matt Klentak said. "We'll pull out of it. We will. That's what talented players will do. I'm not going to tell the fans they shouldn't be frustrated. We've gone through a tough stretch."
Charlie Blackmon hit a two-run double and DJ LeMahieu had an RBI single in the third for a 3-0 lead that was all the run support Hoffman needed. Arenado's 12th homer of the season came in a four-run ninth that blew the game open.
Phillies: Triple-A second baseman Jesmuel Valentin could miss the rest of the season with a separated shoulder that will require surgery. Valentin, son of former major leaguer Jose Valentin, was originally hurt in winter ball and recently aggravated the injury.
Michael Saunders (batting .232) was dropped from the middle of the order to eighth. Saunders, an All-Star with Toronto last season, had only four homers and 15 RBI in a disappointing first two months with Philadelphia. Klentak supported manager Pete Mackanin's decision to bump Saunders in the order. "At the same time, we still have plenty of confidence that Michael's going to get himself out of this," Klentak said. The Phillies still had only three hits for the second straight game.
Klentak said there was no thought of moving scuffling starter Vince Velasquez into the bullpen. Klentak also said pitching coach Bob McClure's job is safe.
Rockies: RHP German Marquez (2-2, 4.34 ERA) takes the mound in his ninth career start.
Phillies: RHP Zach Eflin (0-1, 4.25 ERA) allowed seven runs in his previous outing and looks to win for the first time in seven starts.
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