The visitors slipped two goals behind at the Hawthorns thanks to a first-half double from Shane Long, but Karim El Ahmadi and Ashley Westwood struck back after the interval to rescue a draw in the West Midlands derby.
Lambert was proud of the renewed energy shown by his charges in the second 45 minutes.
"I thought the second half we were fantastic," he told Sky Sports. "I thought we were terrific the way we got going, really resolute.
"To be fair in the first half we were down 2-0 in the first 10 minutes and were just thinking we need to hang in until half-time.
"Second half, I thought they (his players) were outstanding.
Lambert introduced Fabian Delph, Andreas Weimann and Gabriel Agbonlahor 12 minutes into the second period, and was quick to praise the trio's contribution to the fightback.
"We spoke about it and thought we had to get them on pretty quickly," he continued.
"We were actually going to wait a bit longer, but we thought we needed to get a goal.
"The three of them made a huge contribution.
"All credit to the three of them. They only started training on Friday (after returning from injury) and I thought they were outstanding.
"I don't think anybody can label our team for lack of character. Especially here in this atmosphere. I've got nothing but praise for them.
The Scot reserved special praise for goalscorer Westwood.
"I thought Westy took the game by the scruff of the neck. His strike, I thought, was fabulous.
"I thought he was terrific for us."
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