PHOENIX -- The Arizona Diamondbacks and Colorado Rockies meet in a three-game series starting Friday in a matchup of National League West heavyweights.

Just as everyone expected.

Well, maybe some of the two teams' players and their immediate families. The Los Angeles Dodgers and San Francisco Giants were universal picks to top the division before the season.

Instead, Arizona (15-9) took over the division lead by a half-game by beating the San Diego Padres 6-2 on Thursday. Colorado (14-9) slipped to second in the extremely early-season standings after losing its third straight to the Washington Nationals, 16-5.

Among the challenges for the Rockies will be containing the D-backs' running game. After watching Arizona run nearly at will this week, San Diego manager Andy Green called the Diamondbacks "the best running team in baseball. Milwaukee is probably right behind them.

"Milwaukee might end up with more (stolen) bags. Arizona's success rate is going to be higher."

The D-backs stole two more bases Thursday to raise their major-league-leading total to 27 this season.

"It's a challenge for us," Green said. "It's good for us to go through it early in the season because it's an eye-opener to see how easy it is for them to take bags on some of our guys."

The Friday game will match Diamondbacks strikeout artist Robbie Ray (2-0, 3.42 ERA) against Rockies rookie Kyle Freeland (2-1, 3.32 ERA).

Ray went 8-15 with a 4.90 ERA last year but set career highs in starts (32), innings (174 1/3) and strikeouts (218).

The strikeout total ranked tied for No. 9 in the majors, and his 11.25 strikeouts per nine innings trailed only Jose Fernandez (12.49) in the National League.

The key for Ray is to be efficient enough to last deep into games. He has been helped by early-count outs in recent starts, though he also seems to be winning recent battles on 3-2 counts.

"(That) has allowed him to work deeper into games," manager Torey Lovullo said. "The stuff is still electric. The fastball, the breaking ball, the combination of those two pitches has been tremendous, and at times he's overmatched some really good offensive teams."

In his most recent start, Ray gave up five runs on nine hits in 5 1/3 innings in an 11-5 win over the Dodgers.

Freeland heads into his fifth major league start coming off a big outing. He threw seven scoreless innings in an 8-0 shutout of San Francisco on Sunday, allowing six hits while walking one and striking out three. Freeland recorded 12 outs on ground balls.

"His best stuff is down in the strike zone with movement down," Rockies manager Bud Black said after the game. "When you're throwing the ball in the low 90s with action down, you're going to get grounders."

Freeland, 23, has pitched in four big-league games, all starts.

"You learn at home and you learn on the road," Freeland told the Denver Post. "It's about being comfortable in all situations."

The Rockies hope Freeland can stop a stretch of subpar pitching that saw the Nationals put up 42 runs en route to winning the last three games of the midweek series at Coors Field.

While Freeland will be facing the Diamondbacks for the first time, Ray is 2-1 with a 5.30 ERA in seven career starts against the Rockies.

Both teams will feel confident if the game is tight. The Rockies have been great in one-run games, producing a big-league-best 7-0 record. The last team in the majors to start 7-0 in such games was the 2006 Houston Astros. Last year, Colorado was 12-20 in one-run games.

Arizona is 4-1 in one-run contests.