The Seattle midfielder scored the first goal, assisted on the second and helped set up the third as the Sounders broke loose during the second half and extended their two-month unbeaten streak with a 3-0 victory against the Atlanta Silverbacks at Qwest Field.

Seattle now is undefeated in its last 11 USL First Division games (9-0-2) and its last 14 overall (12-0-2, which includes a pair of U.S. Open Cup victories and a 2-1 decision against English Championship club Preston North End in a friendly).

The last time the Sounders came up short was in a 1-0 loss to Montreal on June 23 at Qwest.

Wednesday’s victory, in front of 3,691 fans, helped widen the lead ahead of Portland atop the standings. Seattle is now 13-5-6 with 45 points, four in front of the Timbers (11-4-8, 41), who play host to Charleston on Thursday. The Sounders play host to the Battery on Sunday afternoon at 5.

Seattle already has clinched a playoff spot. Atlanta (10-8-6, 36 points) missed a chance to do so, but remains very much in the running for a postseason bid.

After a scoreless first half, O’Brien, who converted a penalty kick last Friday to help the Sounders beat the California Victory on the road, 1-0, put Seattle on the board at the 46:28 mark. Roger Levesque, who had control of the ball in the box and probably could have taken the shot, instead left it off for O’Brien, who fired from 12 yards away. His shot hit an Atlanta defender, flew over Silverbacks goalkeeper Ryan McIntosh and settled into the back left side of the net.

Near the end of the 81st minute, O’Brien took a corner kick from the attacking left side. Seattle defender Zach Scott went up for a header, but it was deflected. The ball flew out toward the left wing, where O’Brien was waiting. Standing just outside the box, he set up as if he was taking another corner kick, curling it goalward, and Graham went up and hammered a header toward the back right side.

Just 2 ½ minutes later, O’Brien had the ball at the top of the penalty area. He sent it through to Sakuda, whose shot was blocked by McIntosh. But the Atlanta keeper was unable to latch onto the ball, and Levesque ran onto it and drilled it in at 83:13.

Atlanta came into the game on a five-match unbeaten streak, and had scored three or more goals in six of its previous 23 games this season. But the Silverbacks came up empty against Seattle both times, having played to a 0-0 tie against the Sounders on June 9 in Georgia.

The first half ended scoreless, but not for the lack of constant up-and-down-the-field play. Atlanta had four corner kicks, the second of which sailed right across the goalmouth, but too far from any of the Silverbacks attackers.

The Sounders got their attack dangerously into the box five times, only to come away empty. Graham had a header across the goalmouth early in the fourth minute that as saved by Silverbacks keeper McIntosh. Then at the 10:45 mark, Josh Gardner tried to get the ball to Levesque, but it was knocked down. Sakuda ran onto the loose ball, but drilled it wide right.

In the 22nd minute, Gardner, on a direct free kick 28 yards up from the net, lofted it over a four-man Atlanta wall toward the right post. But McIntosh was waiting right there to pull it in.

A 1-2-3 connection from O’Brien to Levesque to Sakuda led to a 12-yard try by Sakuda that went over the top early in the 30th minute. Then during stoppage time, O’Brien got the ball to Levesque, who was playing right in front of the 6-yard box. But Silverbacks defender Matt Bobo was there and got the ball back to his keeper.

Sounders 3, Silverbacks 0

First half -- None.

Second half -- 1, Sea: Leighton O’Brien, from Roger Levesque, 47th minute; 2, Sea: Taylor Graham, from O’Brien, 81st; 3, Sea: Levesque, unassisted, 84th.

Shots -- Atl 11, Sea 9. Saves -- Atl (Ryan McIntosh) 1, Sea (Chris Eylander) 1. Corner kicks -- Atl 4, Sea 5. Offsides -- Atl 1, Sea 2. Fouls -- Atl 11, Sea 6. Cautions -- Atl: Luis Liendo 31st minute; Atl: Tony McManus 64th. Sea: Noah Merl 66th; Levesque 68th; Danny Jackson 75th. Ejections -- None. Attendance -- 3,691.