The NL East-leading Washington Nationals haven't been this far above .500 since 2005.
The Colorado Rockies are at their lowest point since that same season.
Coming off an abbreviated outing, Nationals All-Star right-hander Stephen Strasburg will try to avoid losing three straight starts for the first time in Friday night's series opener against the visiting Rockies.
Down by four runs in the seventh inning, the Nationals (48-32) rallied to beat San Francisco 6-5 on Thursday and extend their winning streak to four.
Bryce Harper, who finished third in fan voting for the final NL All-Star spot, tied the game in the ninth with a single, then scored the final run on Adam LaRoche's grounder when the Giants botched a potential inning-ending double play.
"Not the way we drew it up, but we will take it,'' LaRoche said.
Washington is 16 games above the break-even point for the first time since it was 52-36 on July 13, 2005. The Nationals finished that season 81-81 - still their only non-losing year since relocating from Montreal following the 2004 campaign.
The Nationals will try to extend their season-best five-game home winning streak - their best such stretch since a seven-game surge May 31-June 18, 2011 - with Strasburg (9-3, 2.81 ERA) making his final start of the first half.
The Nationals ace will make his All-Star debut Tuesday in Kansas City, and there's a chance he'll be named the starter by NL manager Tony LaRussa. For now, though, he must try to rebound from back-to-back defeats.
He lasted just three innings in Saturday's 7-5 loss at Atlanta due to heat-related issues. Pitching on Atlanta's hottest day on record, Strasburg lasted three innings - tied for the shortest of his 33 career starts.
"The problem was that he was totally dehydrated," manager Davey Johnson said.
Strasburg had other issues in his previous outing, a 4-2 loss in Denver on June 25 when the Rockies (31-51) scored three runs off him in six innings and prevented the right-hander from becoming the first Nationals pitcher to win seven consecutive starts.
Colorado, though, has now lost five of six to fall 20 games below .500 for the first time since it finished 2005 with a 67-95 record.
Since hitting .344 and scoring 25 runs in their four-game split with Washington from June 25-28 and plating 10 more to win their following game, the Rockies have totaled 13 runs in their last six contests.
After dropping three of four at St. Louis, Colorado will try to get back on track with Drew Pomeranz (0-3, 3.72) making his second start since being recalled from Triple-A Colorado Springs. The left-hander threw six innings of two-hit ball and allowed only one unearned run Sunday, but got charged with a 2-0 loss to San Diego in his first major league appearance since May 7.
"Our starting pitcher put on a clinic today on pitching effectively inside,'' Rockies manager Jim Tracy said.
Colorado right fielder Tyler Colvin is batting .343 with four homers and 14 RBIs in his last nine games - a surge that began when he went 6 for 11 with a homer and six RBIs in the final two games of last month's Nationals series.
All-Star teammate Carlos Gonzalez was 8 for 16 versus the Nationals in June.
Washington's Michael Morse and shortstop Ian Desmond, a first-time All-Star, both went 9 for 19 against Colorado last month, while third baseman Ryan Zimmerman had seven hits in 19 at bats and led the team with seven RBIs.
The Nationals have lost 10 of 13 at home to Colorado since the start of 2008.