It was the second Saturday in succession that Gareth Evans put Pompey ahead from the penalty spot.
And just like last weekend’s Bristol Rovers stalemate, another late goal conceded meant three points became one.
Matty Taylor’s header on 90 minutes ensured Oxford left a windy Fratton Park with a share of the spoils.
Evans had earlier emphatically converted from 12 yards following Elliott Moore’s clumsy challenge on Ben Close.
There were plenty more chances for the dominant hosts and the midfielder was frustrated that they could not take more of them.
He said: “That’s the second game in a row now where we’ve got to the end of the game and it feels more like a loss.
"That’s the second game in a row now where we’ve got it the end of the game and it feels more like a loss."
“We’d got ourselves into a really strong position, having dominated both before and after the interval.
“But we didn’t quite manage to see it out yet again and so you’re left feeling like it’s a defeat rather than a draw.
“I felt like we were on top throughout the game and definitely created the better goalscoring chances.
“After going ahead, we spent the majority of the rest of the half looking for that second goal that never quite arrived.
“Another one would just have killed the game off and we were searching for it, but unfortunately it wouldn’t come.”