Traustason was sent off for New England 14 minutes after the break for his second booking in the space of four minutes when he pulled down Nathan Harriel.
The personnel-challenged Union tried to pile on the pressure once they got the advantage. But their attempts at Knighton's goal rarely suggested true danger, on a night Philadelphia missed seven players to international call-ups, plus Ilsinho and Sergio Santos to injury.
New England's Gustavo Bou missed out with a late-developing injury, but Revs captain and MLS assist leader Carles Gil made his return in the 66th minute after missing all six August matches due to a muscle injury.
Union summer loan signing Matheus Davo made his MLS debut off the bench six minutes later.
- 33' - NE - Matt Polster | WATCH
- THE BIG PICTURE: New England finished the season series with a 2W-0L-1D record against the same Philadelphia side they knocked out of the Audi 2020 MLS Cup Playoffs. But it's fair to say both Revs' wins might not have been an informative playoff preview. Key players on both sides were absent in this one. During a 2-1 New England home win on May 12, Philly manager Jim Curtin rested a host of regulars for a midweek trip.
- MOMENT OF THE MATCH: It wasn't necessarily the prettiest goal. But Polster's ability to get the better of two markers at the back post was enough to lift the Revs to an MLS best-tying seventh away victory.
- MAN OF THE MATCH: Brad Knighton. His best save was probably the 61st-minute denial of Paxten Aaronson from distance. And while he wasn't required to produce the spectacular, his consistency while Turner is on World Cup qualifying duty shouldn't be taken for granted.