Martinez scores again as Atlanta beats Portland 2-0
Atlanta (14-9-3) has won three straight and five of its last six games. United moved atop the Eastern Conference standings, even on points with Philadelphia but ahead on total wins.
"I'm so happy for the team, for the three points, and we have to keep going," Martinez said.
Portland (11-10-4) had won two in a row. It was the third of a 10-game homestand for the Timbers, who started the season with a 12-game trip because of construction at Providence Park. Fighting to stay in playoff contention, the Timbers hope to use the homestand to climb in the standings down the stretch.
It was a rematch of last year's MLS Cup final. United, in just its second year in the league, defeated Portland 2-0 in Atlanta for the championship.
On Wednesday, Martinez scored on a penalty kick in the 65th minute and United gave MLS rare bragging rights over Liga MX with a 3-2 victory over Club America for the Campeones Cup.
Martinez scored in the 46th minute against the Timbers, a blast from 20 yards out that goalkeeper Steve Clark could only watch sail into the net.
"You've got to give credit to them, because that second goal, I think it was cold water thrown at us, and it became difficult," Timbers coach Giovanni Savarese said. "We were still able to make it difficult and go at them, but unfortunately we couldn't find the right moment to capitalize."
United went up in the 14th minute. Atlanta's corner kick was batted around in front of Clark before Leandro Gonzalez Pirez tapped it in.
It appeared that Brian Fernandez responded for the Timbers in the 23rd minute, but it was called offside and there was no VAR review.
In the 35th, it looked as if Fernandez had an open shot from about three yards out that he chipped over the bar. The offside flag again went up, but he still kicked a goal post in frustration.
Fernandez leads the Timbers with 10 goals in his 13 league matches.
Portland upped the pressure in the second half. Atlanta goalkeeper Brad Guzan made a tremendous save in the 65th minute on Julio Cascante's header off a cross from Diego Valeri. It was Guzan's league-leading 12th clean sheet of the season.
"A win is always satisfying, of course. That's the most important thing," United coach Frank de Boer said. "But you look also at how you get the win. I think we fully deserved to get the win."
Jorge Moreira was handed a yellow card in the first half, meaning he'll have to sit out of Portland's rivalry match Friday against the Seattle Sounders.
Atlanta visits Orlando City on Friday.