Rockies 8, Nationals 3: Tyler Colvin hit a pair of two-run homers in his first start of the season and Carlos Gonzalez's three-run shot capped a five-run fifth inning as host Colorado took the opener of a three-game series.

Colvin's first homer started the fifth-inning outburst and Troy Tulowitzki added two hits to raise his average to a National League-leading .353 for Colorado. Jhoulys Chacin (4-3), who was 0-3 in his last seven starts, won for the first time since April 19 after yielding seven hits and two runs in five innings.

Denard Span hit a two-run double in the second inning for the Nationals, who lost for the seventh time in their last 11 games. Dan Haren (4-8) shut out the Rockies for four innings and retired 10 in a row at one point before allowing five runs and eight hits in five innings en route to losing his third straight start.

Wilin Rosario led off the fifth inning with a walk before Colvin's towering drive slipped over the wall just inside the right-field foul pole. After Jordan Pacheco singled with one out, Dexter Fowler followed with a double before Gonzalez's opposite-field blast - his 18th - made it 5-2.

Washington trimmed the deficit to 5-3 on Ian Desmond's RBI single in the eighth before Colvin's second homer - and second of the season - followed Rosario's leadoff single in the bottom half and DJ LeMahieu scored on a double-play grounder to complete the scoring.

GAME NOTEBOOK: Haren has allowed a major league-high 17 home runs this season. ... Rockies RF Michael Cuddyer missed his fourth straight game because of a left rib-cage injury. ... Colvin has spent the majority of 2013 with Triple-A Colorado Springs, where he hit .293 with nine home runs and 29 RBIs in 55 games.