Walker Zimmerman forced extra time with a 91st-minute goal and scored the clinching penalty kick to help top-seeded FC Dallas reach the MLS Cup Western Conference finals with victory Sunday night over the Seattle Sounders in their two-game series.

FC Dallas won 4-2 on penalty kicks after three lead-changing goals in the final 10 minutes of regulation time and 30 scoreless minutes of extra time.

The result after first the 180 minutes of the two-leg series were ties in both the aggregate score (3-3) and away goals (1-1).

The fourth-seeded Sounders, having won the first leg 2-1, tightened their defense to hold the series edge for the first 83 scoreless minutes.

Tesho Akindele broke through in the 84th, heading home Je-Vaughn Watson's cross.

The 2-2 aggregate score would have been enough for FC Dallas with the away goals tiebreaker, but the Sounders tied the game and took back the series lead when Chad Marshall headed in Marco Pappa's corner in the 90th.

Less than a minute later, Walker Zimmerman made it 2-1 for FC Dallas with a turnaround header which forced the two 15-minute, extra-time periods.