Kenny Jackett praised Pompey's resolve as they dug in for victory at AFC Wimbledon.
The Blues made it seven wins and a draw on the road with a 2-1 success at Kingsmeadow.
That ensured they remain three points clear at the top of League One in a match they dominated for long periods.
Tom Naylor (23 minutes) and Gareth Evans (31) handed Pompey a 2-0 lead at half-time.
James Hanson's 63rd-minute strike made it a nervy finale, however, as the Blues were made to battle for victory.
Jackett said: 'I felt for an hour we were well in control.
'We got ourselves in a good position in the first half and it was something similar in the first 15 minutes of the second.
'We had chances and opportunities and had the ball in good situations.
'But they got an excellent goal through Hanson and it made the afternoon harder than we would've liked.
'We dug in, defended and found a way of getting over the line.'