Gage Guerra scored a crucial last-gasp equaliser as the Portland Timbers defeated San Diego FC 3-2 on penalties to force a Game 3 decider in their first-round MLS Cup Playoff series.

Having lost the opener 2-1 last week, the Timbers were staring down the barrel of an exit as goals from Amahl Pellegrino and Hirving Lozano cancelled out Kristoffer Velde's 18th-minute opener at Providence Park.

But Guerra, on as an 86th-minute substitute, met Ariel Lassiter's cross in the eighth minute of injury time to force a penalty shoot-out.

There were five missed attempts between the two teams before Antony scored the winner, which ensures there will be a decider in this series.

Supporters' Shield winners Philadelphia Union became the first team to book a spot in the Eastern Conference semi-finals as a convincing 3-0 win at Chicago Fire secured a 2-0 sweep.

Tai Baribo scored twice, and Bruno Damiani was also on target in the first half as the Union booked an Eastern Conference semi-final date with either Charlotte FC or New York City FC.

That series is going to the wire after Charlotte FC won Game 2 7-6 on penalties after a goalless draw at Yankee Stadium.

Kristijan Kahlina made the decisive save from Agustin Ojeda's spot-kick, having made five saves in regulation time to keep his side alive ahead of the decider at Bank of America Stadium.

The Vancouver Whitecaps progressed to the Western Conference semi-finals after late drama in their Game 2 contest with FC Dallas.

Ralph Priso scored a stoppage-time leveller to secure a 1-1 draw after Petar Musa's 25th-minute opener for Dallas at Toyota Stadium.

The Whitecaps went on to win the shoot-out 4-2, with Patrickson Delgado and Nolan Norris failing from the spot for Dallas.

Data Debrief: Antony influential, Union register another shut-out

Antony not only scored the winning spot-kick for the Timbers but also provided the assist for Guerra. He now has seven in MLS this season, the most of any Portland player.

The Union have built a lot of success off defensive solidity this season, and now have 15 clean sheets from 36 games – the highest in the league.

Indeed, that tally is one higher than Charlotte's, who took their number of shut-outs to 14 against NYCFC.

The Whitecaps have now scored in 15 straight MLS games, which represents their longest scoring streak in the competition since at least 2011.