Hawpe's two-run shot to center field capped a three-run rally against Redding (8-8) with two down in the fifth. Seth Smith singled and scored when Matt Holliday sailed a double over the head of center fielder Lastings Milledge, tying the game at 2 on what could have been the third out. Hawpe followed with his 20th homer.
"One play changes the game," Redding said, referring to the ball that eluded Milledge. "It's one of those situations where we should have won this game 3-1. The second home run to Hawpe should never have happened. ... Any time you give up runs with two outs, it's frustrating."
Milledge acknowledged he mistakenly broke in on Holliday's liner, which was hit directly at him. His retreating, last-second leap wasn't high enough to snag the hit.
"It kind of rose on me," Milledge said. "I didn't make the play [and] I should have made the play. ... It's just a play that got away from me."
Colorado has connected in 10 consecutive games, a season high. Twelve of Hawpe's homers have tied a game or put the Rockies ahead.
"Those are situations you want to be in," Hawpe said. "To be able to change a game is something special. If I get that opportunity, I'm really looking forward to it."
Colorado manager Clint Hurdle has become familiar with the way Hawpe can change a game when he's on a hot streak. Since July 5, Hawpe is hitting .438 (50-for-114) with nine homers and 30 RBIs in 36 games.
"Brad has been in one of the most consistent zones that he's been in in a long time," Hurdle said. "He's got a history of being somewhat streaky, but this has been consistent -- day-to-day-to-day."
The Rockies won for the third time in nine games. Last week at Coors Field, Washington took three-of-four from Colorado.
The Nationals have lost eight in a row. With another loss to the Rockies on Saturday, the Nationals would match their longest skid of the season.
Jorge De La Rosa (6-6) went six innings, allowing three runs and six hits. He had been moved to the bullpen, but returned to the rotation Friday night after an injury to ace Aaron Cook made the Rockies juggle their rotation. Cook is scheduled to start on Sunday.
"He battled. He was grinding from the start until the time he came out," Hurdle said of De La Rosa. "He was able to make pitches when he had to. His command was an enemy and it was a friend."
In the seventh, pinch hitter Willy Taveras singled and stole second, recording his 54th steal, a new franchise record. The previous mark of 53 was set by Eric Young in 1996. Taveras later swiped No. 55 in the ninth.
The Nationals, who had been shut out in three of their previous seven games and 18 times overall this season, took a 1-0 lead in the first. Emilio Bonifacio sliced De La Rosa's first pitch down the left-field line for a double, then scored on Ronnie Belliard's single to right-center.
Redding retired the first seven Colorado hitters in order before Tulowitzki hit his fourth homer to center off an 0-2 fastball. It the first home run since July 2 for Tulowitzki, who had 24 last year.
Washington retook the lead in third when Belliard drew a leadoff walk, moved to second on a wild pitch and scored when Ryan Zimmerman poked a single into right field.
The Rockies rallied for three runs off Redding in the fifth, erasing Washington's 2-1 lead.
Aaron Boone's RBI groundout in the sixth made it 4-3.
Redding pitched six innings, losing for the fifth time in six starts. He gave up four runs and seven hits, walked one and struck out five.
"He missed his location on a couple of pitches," Nationals manager Manny Acta said of Redding, hinting that his starting pitcher had to share the responsibility for Holliday's double.
"On the one on Holliday, they were supposed to elevate the ball to him and they left it right over the plate. He's a very good hitter and he hit it very hard."
Washington has lost nine straight one-run games. ... Colorado's home run streak is its longest since 2006, when the club connected in 11 consecutive games from April 19-30. ... Tulowitzki's homer snapped a 14-game drought without an extra-base hit. ... Since July 3, Fuentes is 10-for-10 in save opportunities and has a 1.15 ERA. ... Nationals SS Cristian Guzman sat out his second straight game with a sore left thumb.