Ibrahimovic scored and provided an assist as the Galaxy returned to second in the Western Conference courtesy of a 2-0 win over Sporting Kansas City.
The Swedish star headed a cross into the path of Favio Alvarez to nod in the opener in the 55th minute.
Ibrahimovic, returning from a two-game suspension, sealed the win late on, volleying in an Uriel Antuna cross for his 10th goal of the season.
The Galaxy are six points adrift of Los Angeles FC, while Sporting sits 11th in the Western Conference, having struggled with injuries in the early part of the season.
Franco Escobar's fine 23rd-minute finish put Atlanta ahead, but the Five Stripes had to wait until late on to wrap up their victory.
Martinez scored twice in additional time to take his tally to eight MLS goals this campaign.
Wayne Rooney provided an assist but United were held to a thrilling 3-3 draw at home to Chicago Fire.
Philadelphia, meanwhile, played out a 1-1 draw against the struggling Colorado Rapids.
MLS returns to action on Friday with Vancouver hosting Toronto FC, with a full round of matches to follow on the weekend.