Teenage forward Jed Wallace bagged his third goal in three matches after three minutes to put Pompey ahead but Keith Keane's stunning volley after 77 minutes levelled for Preston.
Portsmouth rode their luck at times - Jack King headed against the bar and Joe Garner hit a post before North End eventually equalised - but they have now lost just once in seven matches.
They remain in the relegation zone, however, but Whittingham is adamant his weary troops will battle to the end against Tranmere on Easter Monday.
"It's a point gained really, considering the performance. I think on the other side of things it shows how far this group of players has come," said Whittingham.
"I thought we battled against everything Preston threw against us and it took a good goal to beat our goalkeeper.
"I think everybody could see we weren't playing at our best but I think we were dogged and we had a couple of strokes of luck where they hit the bar and the post.
"The goal gave us something to keep hold of but we didn't play at our best like our fans want to see. It was a dogged performance and they dug in.
"Before the game we didn't think they were tired. We are where we are in terms of a small squad but the players that have come in have put in a good shift and put in some good work for the fans."