Carlos Vela celebrates LAFC’s victory over the LA Galaxy. (Kelvin Kuo-USA TODAY Sports)

The new single-elimination MLS Cup Playoffs delivered continued drama and momentum swings during Wednesday and Thursday night’s conference semifinal matches.

The field was trimmed in half from eight teams to four with Atlanta United, the Los Angeles Football Club, Seattle Sounders FC and Toronto FC advancing to next week’s conference finals. Among them, the last three MLS Cup champions are still alive: Atlanta, Toronto and Seattle.

For the first time in their six meetings and in another high-scoring affair, No. 1 LAFC won a history-defining El Tráfico match, 5-3, against their crosstown rivals fifth-seed LA Galaxy with goals from both club’s superstars in Carlos Vela of LAFC and Zlatan Ibrahimovic of the Galaxy. The eight goals tied an MLS postseason high.

No. 1 LAFC will host No. 2 Seattle Sounders FC in the Western Conference final Tuesday, Oct. 29 (10 p.m. ET, ESPN / ESPN Deportes / TSN / TVA Sports 2).

No. 2 Atlanta United advanced after goals from Julian Gressel and Josef Martínez sealed a 2-0 home victory over the Philadelphia Union. Continuing their title defense as reigning MLS Cup champions, Atlanta returns to the Eastern Conference final in consecutive seasons.

No. 2 Atlanta will host No. 4 Toronto FC Wednesday, Oct. 30 (8 p.m. ET, FS1 / FOX Deportes / TSN 1/4 / TVA Sports).

Seattle Sounders FC became the final team to qualify for Concacaf Champions League, which will be ots sixth CCL appearance. The slot belonging to the MLS Cup champion will be secured by either LAFC, Atlanta, Toronto FC or Seattle pending results of the MLS Cup Playoffs.

Should a CCL-qualified club (LAFC/New York City FC/Atlanta) or a Canadian club (Toronto) win MLS Cup, the club with the highest point total, regardless of conference, would qualify for CCL. Based on final regular season standings, Seattle has qualified for the tournament.

The final ranking of the U.S.-based MLS qualified clubs will be determined pending results of the MLS Cup. The MLS Cup Champions take the top spot, followed in order by Supporters’ Shield winners, Eastern Conference regular season Champion, Lamar Hunt U.S. Open Cup champion, and any remaining club occupying the fourth and final slot.