Dallas' 10 points leads Major League Soccer. Dallas (3-0-1) is off to its best start since 2006, where it also logged 10 points through the first four games.
''We've started well and we're happy,'' first-year Dallas coach Oscar Pareja said. ''We know where we are and we don't want to think too much about what we have not done before. We're developing a culture of taking it one game at a time, without giving importance to what happened last season or what will happen. ''
Portland (0-1-3), in its fourth MLS season, is off to its worst start in its young history.
The teams played the second half with 10 men apiece after Portland left back Michael Harrington and Dallas right winger Je-Vaughn Watson were ejected for an off-the-ball fight with about five minutes left in the first half. The decision ended Harrington's streak of 1,749 consecutive minutes played for Portland.
Head referee Storin Stoica told a pool reporter that the pair was ejected after Watson struck Harrington and the defender retaliated.
''It was basically just a little shoving match,'' Harrington said. ''Me and Watson were running out (during a goal kick). He kind of took a little push at me - I'm not sure why - and I kind of just pushed him back. It wasn't anything too serious.''
Watson echoed Harrington's thoughts.
''There was nothing there to give a red card for,'' said Watson, who picked up his third career red card. ''Soccer is a competitive sport. He was pulling on me and I was pulling on him, so it was on the ball the first time, so I don't see that's a red card. I was saying before he gave the red card, I was saying, 'if you're going to do something, that's a warning. That's not a red card.'''
Dallas went ahead in the third minute of first-half stoppage time on a Blas Perez header, but the Timbers tied it in the 67th minute when Dallas defender Matt Hedges deflected a Maximiliano Urruti pass into his own net.
The Timbers outshot Dallas 15-9, including 10-5 in the second half, but it was Diaz's late effort that won the game. After the ball fell to him near the top of the box, he dribbled to his right, and then fired a right-footed shot across his body and past the outstretched hands of Timbers goalkeeper Andrew Weber.
''We had chances to go (up) 2-1,'' Portland coach Caleb Porter said. ''At the end of the day I credit Mauro Diaz, who pulled off a play. Players win games. He pulled off a play and that was the difference in the game.''