"Any time it rains here and get those dark skies, you never know what the ball's going to do," said Tulowitzki, who was surprised to watch his 18th homer sail through the downpour and spark Colorado's 8-2 rout of the San Francisco Giants on Saturday night.
Tulowitzki drove in a career-high five runs and Jorge De La Rosa won his career-best sixth straight start as the Rockies moved a game ahead of the Giants in the NL wild-card race.
De La Rosa (8-7) allowed one run on seven hits over 7 1/3 innings with no walks and seven strikeouts. He retired the first 11 batters he faced, six by strikeout, before Pablo Sandoval stroked a double into right field with two outs in the fourth.
"It's exciting to pitch like I'm pitching right now," said De La Rosa, who started out 0-6 this season. "I feel very comfortable right now. I have to keep pitching like I pitched today."
The key to De La Rosa's turnaround is a better tempo and a newfound ability to bounce back quickly from adversity, which limits the big innings that were his undoing the first half of the season.
"I see a guy with some dominant stuff," Tulowitzki said. "I've been telling you guys for a while, if he challenges the strike zone, he's as good as anybody."
Sanchez (3-9) matched De La Rosa inning for hitless inning until Todd Helton led off the fourth with a line-drive single to right for Colorado's first hit.
Right after Helton's single, rain sent the fans scurrying for shelter or umbrellas. Garrett Atkins drew a walk and one out later, Tulowitzki sent Sanchez's first offering into a downpour and over the wall in right-center for his 18th homer and a 3-0 lead.
"To get it out of the park tonight, you had to hit it real well," Tulowitzki said. "I got that one real good. I still wasn't sure. I was still running hard. Luckily, it got out."
The degree of difficulty was high with the steady downpour.
"I don't know how much water he had in his eyes," Rockies manager Jim Tracy said. "The interesting thing about what you're suggesting is the air was somewhat heavy tonight. He really hit that ball and obviously hit it the other way. It took just a great at-bat. When you see Troy Tulowitzki hitting balls with authority that way is when you know he's locked in. That's when he does the most damage."
Sanchez, who entered with a 1.59 ERA in July and left with a 3.27 ERA this month, has given up three home runs in his two starts since pitching a no-hitter against San Diego on July 10.
He allowed five earned runs on five hits over five-plus innings Saturday night, and his worst pitch of the night was the one that didn't tail far enough away from Tulowitzki in the fourth.
"He was ready for it. If you're guessing on a pitch and you get it, you're going to crush it," Sanchez said. "I got him out with a fastball on the first at-bat, so he was looking for it."
The Giants pulled to 3-1 on Sandoval's RBI double in the sixth, but Tulowitzki's run-scoring double in the bottom half of the inning restored Colorado's three-run cushion and chased Sanchez.
Tulowitzki's RBI single off Merkin Valdez in the eighth sparked a three-run outburst after the Giants had pulled to 5-2.
RHP Jhoulys Chacin made his major league debut for Colorado in the ninth, allowing no hits, a walk and a wild pitch and striking out two. ... De La Rosa leads the majors with eight wins since June 1. His six wins in six straight starts matches the franchise record set by Aaron Cook last season.