Will Venable clubbed a grand slam and Nick Hundley added a three-run homer, both off Ryan Dempster. This season was a near reversal of last year for the Padres (71-91), who actually won eight of their last 12 games, but still finished in last place in the NL West.
In 2010, San Diego was 90-72, but this year produced a fifth straight season without making the playoffs.
LeBlanc (5-6) allowed five hits and a pair of runs.
The 2011 season for the Cubs (71-91) was a breakout one for Starlin Castro. The 21-year-old shortstop became the youngest player in NL history to top the league in hits with 207.
Dempster (10-14), who was charged with eight hits and a season-high nine runs over 5 2/3 innings, lost his last six decisions.
"I don't really like to finish the season that way," Dempster said. "But I'm proud of the way I battled all year."
LeBlanc doubled in the third and scored on Cameron Maybin's double to left field. Maybin stole third, and two batters later Hundley homered to left field.
Tony Campana singled in Jeff Baker in the fourth, but the Padres got a run back in the bottom half thanks to a Castro fielding error when he bobbled the ball on a grounder by Andy Parrino.
Castro had a sacrifice fly in the fifth, but the Padres made it a rout in the sixth. Parrino and LeBlanc singled before Maybin walked, leading to Venable's first career grand slam, a shot to left-center.
"It was really nice for me personally to end on that note," Venable said.
Castro reached base safely in his final 40 games...Maybin stole his 40th base of the season in the third inning. He is the ninth Padre to steal 40-or-more bases in a season, the 13th time it's happened for San Diego and first since first base coach Dave Roberts stole 49 in 2006...Chicago's Steve Clevenger pinch-hit in the fifth inning and came up with a single, his first major league hit.