SAN DIEGO -- On Aug. 10, the Arizona Diamondbacks departed Phoenix on a nine-game road trip that was packed for opportunity.

All the games would be played against teams trailing their respective divisions -- Cincinnati, Texas and San Diego. But the first two stops didn't produce the expected results. The Diamondbacks lost two of three in Cincinnati and split a short two-game series against the Rangers.

But they got back on track Thursday night in the first contest of a four-game series at Petco Park, defeating the Padres 5-1 behind Clay Buchholz's 10th career complete game.

The Diamondbacks hope to protect -- or extend -- their 1 1/2-game lead over Colorado in the National League West on Friday when they send Robbie Ray to the mound in a duel of left-handers.

Ray (3-2, 4.83 ERA) will be opposed by Padre rookie Joey Lucchesi (6-6, 3.45).

Arizona's 4-0 record at Petco Park this season has given it an 8-3 advantage over the Padres with eight games to play -- including the final three games of the season in San Diego when Arizona might need wins to advance to the National League playoffs.

Thus far, the Diamondbacks have a better record against the Padres than any of their division rivals. And the ability to beat the Padres could ultimately decide who wins the National League West.

The Padres and Ray are no strangers. Friday night will mark the 11th time that Ray has faced San Diego in his career. He is 4-4 against the Padres with a 4.26 ERA. This will be his second start against the Padres this season. On July 7, Ray started Arizona's 20-5 victory over the Padres. But he didn't get credit for the win, leaving after allowing four runs in 4 1/3 innings.

Ray has been at his best in his first eight road starts this season, going 2-1 with a 2.70 ERA and holding opponents to a .199 batting average while striking out 54 in 40 innings.

And Ray has been very effective in his four previous starts at Petco Park, going 2-1 with a 2.70 ERA.

On the season, Ray has pitched 76 1/3 innings in 15 starts -- allowing 42 runs (41 earned) on 70 hits and 39 walks with 101 strikeouts for a .246 opponents' batting average and a 1.43 WHIP. But he has allowed two or fewer runs in three of his last four starts.

The Padres have won three of the four games the 25-year-old Lucchesi has started since he returned from Triple-A El Paso on July 23 -- a move that was made to slow his accumulation of innings. Lucchesi worked six shutout innings in his most recent start against Philadelphia on Sunday, holding the Phillies to two hits and three walks.

Over his last eight starts, Lucchesi has a 2.95 ERA with a 3-3 record, and the Padres went 4-4 in those games. The Padres have gone 8-10 when Lucchesi starts this season.

Lucchesi has started three games against Arizona this season, going 0-3 with a 6.75 ERA in those games.