Portsmouth blew a golden opportunity to snatch the three points when striker Izale McLeod crashed a penalty against the crossbar after 14 minutes.
Westley said: "We made a number of changes to the side and it was always going to be difficult for us to show genuine organisation.
"On the whole, the players worked hard at their organisation over the 90 minutes, they worked hard to stay solid and we came away with the clean sheet, largely due to the attitude and work rate of the team.
"The clean sheet is always positive. We lost two games after Keane and Laird went out of the backline and we've had to do a lot of re-shaping to try and get our back four back together.
"When you're reshaping that and trying to get it to work well, sustaining all the momentum in your forward game is never easy.
"But we had enough of a forward game to create some good moments and could have easily won."