Richard (4-2) scattered seven hits and struck out six, yielding only a sixth-inning RBI single to Mike Sweeney in notching his fourth win in his last four starts. He lowered his ERA to 2.73 with his latest win.
Heath Bell survived a scary ninth inning to register his 12th save, allowing hits to Sweeney and Jose Lopez before striking out Milton Bradley and inducing Casey Kotchman to ground out to end the game.
Stairs' mammoth solo shot to right in the fourth inning gave San Diego a 1-0 lead and the Padres added an insurance run in the sixth when Chase Headley scored on a wild pitch by Kanekoa Texeira.
Ian Snell (0-3) absorbed the tough-luck defeat, allowing only one run on five hits over five innings as the Mariners lost for the eighth time in 11 games.