YARMOUTH — James Smith scored on a chip shot 12:05 into the first overtime Tuesday night to lift the Portland Phoenix to a 2-1 victory against the Seacoast United Phantoms in the Premier Development League men’s soccer playoffs.

The Phoenix, who haven’t lost since their opening game in May, are one of the final 16 teams in the 63-team league.

They will play the New York Red Bulls’ under-23 team in the Eastern Conference semifinals Saturday at Elizabeth, New Jersey. Charlotte and the Jersey Express will meet in the other semifinal.

The four conference winners will meet the following weekend for the national title.

The Phoenix beat the Phantoms, based in Portsmouth, New Hampshire, for the third time in five meetings this summer. The Phantoms are the only team to defeat Portland, and they also played to a contentious tie late in the season.

“When it’s winner-take-all like this, it’s so important you look after the fine details, and I think the boys did that tonight,” said Portland Coach Ally Bain.

Play was suspended for nearly an hour in the second half because of lightning.

“The lightning delay presented a few mental obstacles,” said defender Robbie Lentine, who led Windham to the Class A state title in 2011. “I think we did a good job of keeping it together and eventually we came out on top.”

Smith’s goal came on one of the few chances either team had in overtime.

“Keegan (Campbell) made a terrific pass over the defender and I saw the goalie come out, and I thought I could get it over his head,” said Smith, who lobbed a high, arcing shot from 15 yards. “It came back down, and it was nice to see it go into the back of the net.”

The first 30 minutes were uneventful.That changed when the Phoenix were awarded the first two corner kicks of the match 32 minutes in.

On the first corner, Seacoast goalie Dominic DiMaggio dived to his left to punch Peabo Knoth’s blast from just inside the box away.

The Phoenix continued to apply pressure and it paid when Andrew Wheeler-Omiunu, a center midfielder who will be a junior at Harvard in the fall, intercepted a clearing pass, turned and sent a rising shot from 20 yards outside the reach of the leaping DiMaggio.

The Phantoms opened their offense at the start of the second half. In the 53rd minute, an amazing tackle by Campbell prevented A.J. DuBois from walking in alone on goalie Matt Williams.

Six minutes later, DuBois set up Barry McCabe from well inside the penalty area to make it 1-1.

With 18:57 left, play was halted because of lightning.

Three minutes after play resumed, the Phantoms were on the verge of taking the lead when Anthony Grant, the league’s leading scorer, bounced a shot past Williams, but Wyatt Omsberg stepped in to clear the ball away from the open net.

With less than five minutes left in regulation, Wheeler-Omiunu just missed converting Quincy Appah’s cross for Portland.

“It was a tight game, and it always is against these guys,” Smith said. They stayed compact and made it tough for us like they always do.”

NOTES: Brothers Cameron and Wyatt Omsberg were opponents. Cameron, entering his third season as an assistant men’s soccer coach at Bates College in Lewiston, started at center back for Seacoast; Wyatt, a Dartmouth sophomore who led Scarborough to two Class A state titles, entered the game just before the delay … In addition to the Omsbergs and Lentine, former Maine high school players for the Phoenix include midfielder Peabo Knoth, Waynflete; Williams, Cheverus; midfielder Nick Melville, Cheverus; backup goalie Chris Knaub, Yarmouth; and back Andy Murry, Falmouth.