Substitute Gus finally floored Pompey after Harry Redknapp's men came back from 1-0, 2-1 and 3-2 with the winner two minutes from time.
It was the second 4-3 result at the Lane in four days and there was a reality check from the experienced midfielder.
"We have to improve," he stated. "You can't play every game at home and concede two, three or four goals. It's too much.
"Anyway, we were talking in the dressing room and to be fair, if you have to pick one of the games to win 4-3 and one to lose 4-3, we would have to say the Premiership, to get the points, to get better and improve.
"It was probably the youngest team in I don't know how many years, so that is positive news as well."
Gus Poyet insisted the lads kept believing they would come out on top in the latest emotional rollercoaster at the Lane against Portsmouth on Saturday.
In another seven-goal thriller following the FA Cup exit against Manchester City, we led three times only for Pompey to hit back on each occasion.
But this time we prevailed 4-3 as Simon Davies swung in a corner, Dean Richards headed back and Gus, on as substitute, converted from six yards with only two minutes left.
The irony of the scoreline after the City game - and the songs from the visiting supporters after Pompey levelled at 3-3 - weren't lost on the midfielder.
He said: "If you listened to their fans when it went to 3-3, they were singing 'we're going to win 4-3' and perhaps everyone in the stadium thought that.
"We didn't. We kept pushing, kept trying, kept believing.
"First, I'm pleased for the players and especially Deano. Sometimes it happens that you can make a mistake or do something not as good as you want to, then go up the other end and do something for the goal.
"I looked around and everyone was celebrating everywhere and you just can't help those feelings. We were all delighted to get the three points."
I wanted to hit it first time, one touch, I' better that way.,= Soetimes it can be te knee, my bad one, by the way, but it worked. We're all pleased. e've got three points.
Gus Poyet wasn't too lost in the emotion of Saturday's 4-3 win against Portsmouth to admit: We have to improve.