Martin Allen felt the 5-1 scoreline at Fratton Park on Saturday afternoon flattered title favourites Portsmouth who struck twice following Bira Dembele’s dismissal.
The Bees went in front after 27 minutes when John Akinde stroked home a penalty against his former club.
However, Pompey soon levelled through Conor Chaplin and were in front early in the second half when Gary Roberts netted. Carl Baker added a third shortly after.
Things went from bad to worse when Dembele, on his first start following injury, was sent off for a foul on Chaplin in the penalty area.
Josh Vickers saved Roberts’ spot kick but Pompey enhanced the scoreline with late goals from Milan Lalkovic and Danny Rose.
Reflecting on the defeat, just the Bees’ second of the new EFL League Two campaign, Allen said: “I don’t think it was a 5-1 performance.
“We played very well in the first half and we were very unlucky not to go 2-0 up with John Akinde’s free header from a set play – 2-0 would have made a massive difference
“We knew they would come out stronger in the second half. We lost possession twice on the edge of our own box which was disappointing.
“But I thought we played with good control, moved the ball around well and we had some very good performances.
“I certainly can’t go into the dressing room and say it was an awful performance. The players gave everything they have got.”
The dismissal of Dembele was the game’s turning point but it was unclear whether the French centre-back should have been red carded.
Ahead of the new season the rules were changed so that players who commit an accidental foul in the penalty area would only receive a yellow card.
“It was a 50:50 and their player got to the ball first with a little toe,” said Allen of the decision. “He wasn’t in on goal either, the ball went out for a goal kick in effect. Perhaps it was a penalty, but it wasn’t a sending off.
“I will have to sit down with Andrew Adie, our secretary, as quickly as possible as we play Morecambe on Tuesday night. I thought it was a yellow card because the rules have changed.”
The loss of Dembele did not change Barnet’s commitment to attacking Portsmouth and the Bees head coach kept Shaun Batt and Akinde paired together up front in search of a route back into the game.
“At 3-1 with ten men I could have sat everyone back and seen the game out,” said Allen. “But I didn’t want to do that. I kept two up front because I wanted to attack.
“If we got one, we could have put them under pressure in front of their home crowd.
My attitude was: ‘Let’s still go for them.’ We did, we left ourselves open and they punished us.
“They have the players to punish you in the final third. When you’re playing with ten men and two up front you’re going to leave yourself open. Sometimes you have to ride your luck.”