The veteran striker gave Pompey the perfect start by heading in Jed Wallace's 22nd-minute free-kick to claim his first goal for the club.
But that lead lasted just five minutes before defender Shaun Williams struck a brilliant equaliser.
Whittingham said: "David is a very intelligent player and is a good asset for us. I am glad he got his goal because he worked very hard.
"He works really hard in training day in, day out.
"A draw was probably a fair result because we were the dominant team in the first half and they were the better team in the second.
"Our players worked very hard and there were some very encouraging performances out there."