Pompey have received criticism for some porous defending in the opening stages of the season.
But it was a display of resoluteness at the back that provided the backbone for a first league win on the road.
That allowed a Gareth Evans goal on the break and – after Reece James had levelled – stoppage-time header from Ellis Harrison to secure all three points at Doncaster.
And despite being disappointed with a disjointed performance before the break, Kenny Jackett was pleased with his side’s committed showing.
The Blues boss said: “We had to defend – and were more like ourselves at the back than in recent weeks – and try to cause problems on the counter.
“I felt that in the first half we didn’t do enough and couldn’t create, so we had to define those ‘nine’ and ‘10’ roles after the break.
“Ellis came on and his pace was a real threat because when you win the ball back, you’re one or two passes away from a chance. That proved to be the case.
"We also had to soak up a lot of pressure and defended really well. It was heroic at times."
“It was an excellent and well-worked goal on the break from Gareth Evans, who took it really well with his left foot.
“And then it was another assist for the winner from James Bolton – it’s two for him in as many weeks now.
“I’m really pleased for Ellis because it was a terrific header and he put it right in the top corner, giving the keeper no chance.
“There were other chances in the second half and Ben Close had a shot that was kept out by a fantastic save.
“But we also had to soak up a lot of pressure and defended really well. It was heroic at times and that’s often needed away from home.
“Not many sides will come to Doncaster and win this season and we have to keep trying to build if we can.”
Jackett also explained why Ronan Curtis was not included in the matchday squad, having started every previous league fixture.
He said: “Ronan felt his hamstring during training this week. It was tight and so we didn’t want to risk him.
“He’ll have an MRI on Monday and we’ll speak to the Republic of Ireland guys about what they want to do.”