These are fun days for the improving Chicago Cubs.
''This is the nicest I've felt about this team since I've been here,'' said Anthony Rizzo, who was acquired in a January 2012 trade with San Diego.
Chris Coghlan added a solo shot as the Cubs opened a 10-game homestand with their fourth win in five games. Last-place Chicago also improved to 18-13 since May 17 for the best record in the NL in that stretch.
''Everything in this game is contagious, whether it's positive, negative, hitting, defense, pitching,'' Coghlan said. ''I think we're having more team at-bats.''
Jackson (5-7) was removed after 86 pitches due to cramps in his calves, but it was enough to get his first win in four matchups this year against Morton (4-8). The right-handers have faced off more than any other pair of starting pitchers this season in the majors.
Jackson allowed three runs on Jordy Mercer's fifth homer and five hits. He struck out eight and walked two in just his second win in his last six starts.
Alvarez had a chance to tie the game when he came to the plate with two on and two out in the sixth. He took a frustrated hop between first and second as Ryan Sweeney ran down his long fly ball in the biggest part of the ballpark.
Andrew McCutchen struck out with two on in the seventh, wasting another Pittsburgh threat.
''Pitching's been pretty great all year. The offense is coming around, and the defense is coming around as well,'' Jackson said. ''So we're definitely showing a glimpse of what we're able to do. It's just going out and doing it on a consistent basis.''
Pittsburgh rookie Gregory Polanco opened the game with a single to center, extending his hitting streak to 10 games. He is the first NL player to begin his career with such a streak since Juan Pierre's 16-game run for Colorado in 2000.
The Pirates have lost four of five since a four-game winning streak.
Morton retired six in a row before Jackson's one-out single in the third started a string of five consecutive batters reaching safely. Rizzo lined a two-run double into the right-field corner before Castro drove an 0-2 curveball over the wall in left for his 11th homer, moving past his total from all of last year.
Morton jerked his head down in disgust when Castro connected, and then turned around to see where the ball was going. Castro's third homer of the season against Morton gave the Cubs a 5-0 lead.
''I could have gotten the ball down a little bit more,'' Morton said. ''I don't think it was a bad pitch. It was a bad pitch to him in that situation.''
The six runs in six innings were a season high for Morton, who had won each of his last three starts and was 4-1 with a 2.40 ERA in his previous five outings.
Mercer went deep after Jackson walked the first two batters in the fifth, but that was it for the Pirates. Four Cubs relievers combined for three innings of two-hit ball before Hector Rondon worked the ninth for his eighth save in 10 chances.
Jason Grilli pitched the eighth for the Pirates in his first outing since manager Clint Hurdle removed the right-hander from the closer role. Grilli has blown four save opportunities this season after converting 33 of 35 chances a year ago.
''Better rhythm, a better execution of pitches,'' Hurdle said when asked about Grilli's inning.
Hurdle said before the game that Mark Melancon will close for now, and he also could use Tony Watson in save opportunities. ... Cubs president of baseball operations Theo Epstein said he is pleased with Manny Ramirez's impact on the organization so far, and the former major league star could join Triple-A Iowa next week. When Ramirez reports to Iowa, he will be a player-coach for Chicago's top farm club. ... Epstein also said he doesn't forsee a scenario where prospect Kris Bryant joins the major league club this year. ... Pirates RHP Vance Worley (0-0, 0.00 ERA) and Cubs LHP Travis Wood (7-5, 4.48 ERA) face off on Saturday.