DENVER -- Pittsburgh starting pitcher Jeff Locke took a step forward Sunday, but the Pirates again stumbled.
They lost 3-2 to the Colorado Rockies, who completed a three-game sweep, and sent the Pirates on to St. Louis for a key series with a three-game lead over the Cardinals in the National League Central.
Rookie third baseman Nolan Arenado drove in the winning run with a two-out double in the seventh. The victory gave the Rockies their first three-game winning streak since May 21-24. The Pirates were swept in a series for the first time since June 3-5. The Rockies limited the Pirates to seven runs in the series.
"At the end of the day, you look at the three games, they pitched better than us, they hit better than us, they fielded better than us," Pirates manager Clint Hurdle said. "You honestly self-evaluate and move on and get ready to play in St. Louis."
Arenado has shown he likes the challenge of coming through in a key moment. He did it again when he followed a single by Wilin Rosario with a double off Bryan Morris that ended a scoreless streak by Pirates relievers at 18 2/3 innings.
"I knew he had a cutter and a slider," Arenado said. "I was looking for a cutter or slider middle-away. He threw me a first-pitch fastball in. If he would have thrown it again I could've been jammed or not swung. Luckily it was a cutter right over the plate and I was able to put a good swing on it.
Rockies closer Rex Brothers survived a ninth-inning scare for the second straight game.
Brothers, who threw 27 pitches Saturday night, gave up a leadoff single to Neil Walker. Brothers struck out pinch hitter Russell Martin, but Tony Sanchez's double to right-center moved Walker to third.
With the infield drawn in, pinch hitter Jordy Mercer lined out to Arenado. Brothers intentionally walked pinch hitter Gabby Sanchez and got Alex Presley to pop out to Arenado on Brothers' 17th pitch to pick up his 10th save.
Locke worked 5 2/3 innings and gave up three hits, the last a single by Charlie Blackmon that put runners on first and second.
Tony Watson came on to face pinch hitter Corey Dickerson and got him to hit a slow grounder to third baseman Pedro Alvarez, who overthrew first base allowing Yorvit Torrealba to score and tie the game at 2-2.
Locke, who took the mound with a major league leading 1.83 road ERA, had gone 0-1 with a 4.96 ERA in his past three starts, allowing 27 hits in 16 1/3 innings. He gave up a run without benefit of a hit in the third.
Locke hit leadoff hitter Blackmon with a pitch. He stole second, moved to third on a balk and scored on LeMahieu's sacrifice fly.
"(The umpire) said when he stepped off, he didn't clear the rubber," Hurdle said. "His foot was still pointed to first. I don't think it showed that. I thought he cleared the rubber, stepped off."
Locke worked around shortstop Clint Barmes' error and left the bases loaded in the fifth when he got Rosario to ground out. Alvarez's throwing error tagged Locke with an unearned run in the sixth, which began with a leadoff walk to Arenado.
"Today was definitely a step back in the right direction mechanically, mentally," said Locke, who is 9-3 with a 2.43 ERA in 23 starts. "Everything felt back to normal today."
Making his third major league start and his Coors Field debut, Chad Bettis, 24, held the Pirates to two runs and four hits in six innings. He gave up Alvarez's 28th homer in the second and a two-out, run-scoring infield single to Andrew McCutchen in the third.
"A young kid, first start at Coors Field, I thought he handled himself very well," Rockies manager Walt Weiss said of Bettis.
The Pirates, who took four of five games from the Cardinals in late July, are off Monday before beginning their big series Tuesday in St. Louis.
"It will be a day for everybody to unplug, just kind of get away from it for a day," Locke said. "Not that anybody feels like they need to or anything like that. We've played some good baseball here, but not the kind of baseball that we're accustomed to playing right now.
"But every team goes through things like this. If it was seven, eight games and not three, it'd be a different story."
Notes: Rockies C Rosario made his second career start and third appearance at first base where he had played 10 innings prior to Sunday. He started there Sept. 20, 2012, at San Francisco and played two innings at first base this season on July 31 at Atlanta. ... Pirates LF Starling Marte pinch ran in the ninth. He was not in the lineup after getting hit with a pitch and suffering a left hand contusion in the seventh inning Saturday night. ... Alvarez was spiked and suffered a laceration on his left index finger Saturday night but was in the Pittsburgh lineup Sunday. ... With the Pirates off Monday, rookie RHP Gerrit Cole will have his next start pushed back to Friday against Arizona as the Pirates monitor his innings.