SEATTLE — It wasn’t always the prettiest of two-legged ties, but the Seattle Sounders eventually routed El Salvadoran side Santa Tecla on Thursday night, advancing to the CONCACAF Champions League quarterfinals with a 4-0 victory.

The Sounders won the series 5-2 after dropping the first leg 2-1 last week in El Salvador. They now face Liga MX powerhouse Chivas Guadalajara in the quarterfinals, hosting the first leg on March 7 before visiting Mexico the following week.

Thursday night’s victory was not easy, despite the lopsided score. For 45 minutes, the Seattle Sounders looked every bit a shorthanded team essentially in preseason form.

Then came the second half.

Sounders head coach Brian Schmetzer inserted Magnus Wolff Eikrem — signed with Targeted Allocation Money only in late January — at halftime. The 27-year-old Norwegian provided an immediate lift, and it took the Sounders only three minutes of second-half action to find a goal.

Will Bruin opened the scoring in the 48th minute after Nicolas Lodeiro gathered a pass from Gustav Svensson and found Bruin streaking into the 6-yard box. The longtime Houston Dynamo striker slipped into space between the Santa Tecla center backs and tapped a shot past goalkeeper Joel Almeida for the 1-0 lead.

The goal tied the series at 2-2, but thanks to the away-goals tiebreaker the visitors were forced to open up and chase the game — and that opened the floodgates for the Sounders’ attack.

Lodeiro added the second goal in the 68th minute, latching onto a Clint Dempsey cross and sending a soft header past a charging Almeida and bouncing over the goal line.

Chad Marshall put the match — and the series — away in the 82nd minute, rising at the edge of the 6-yard box and heading a Lodeiro corner kick just inside the near post.

Eikrem added the fourth and final goal in the 84th minute off a give-and-go with Clint Dempsey. Eikrem first found Dempsey at the top of the 18-yard-box before charging into the penalty area and one-touching a beautiful return pass into the side netting for the 4-0 lead.

Referee Walter Lopez whistled Santa Tecla for 12 first-half fouls and issued the visitors a pair of yellow cards to boot. Otherwise, the opening 45 minutes went precisely according to head coach Ruben Da Silva’s plan. Packing eight, nine, and even 10 men behind the ball, Santa Tecla successfully neutered a shorthanded Sounders’ attack.

Seattle — playing its first match since striker Jordan Morris tore his ACL last week — took eight first-half shots, but only managed to put two on target. In addition to Morris, the Sounders were without right back Kelvin Leerdam (ankle), center back Roman Torres (leg), defensive midfielder Osvaldo Alonso (quad), and attacking midfielder Victor Rodriguez (quad).

Marshall saw perhaps the best chance of the half in just the 12th minute, latching onto a Lodeiro corner kick but sailing a short-range header over the end line when no teammate ran to the far post. The Sounders controlled possession for the rest of the half, but struggled to find penetrating passes or put the visitors in uncomfortable positions.

Looking forward, the Sounders open their MLS campaign against Los Angeles FC at CenturyLink Field on Sunday.

MAN OF THE MATCH

Nicolas Lodeiro. The Uruguayan playmaker delivered a goal and two assists on the night. He also provided the road goal last week with a stunning 40-yard chip shot.

MOMENT OF THE MATCH

Bruin’s goal. An opening goal from the hosts was always going to open up Santa Tecla, and once the visitors stopped bunkering Seattle’s attack went to work.

MATCH TO FORGET

Joel Almeida. Not all of the goals were his fault, to be sure. But the goalkeeper’s positioning was questionable throughout the night.