The tourists edged a thriller at the Westpac Stadium in Wellington to level the series and set up a crunch decider back in Auckland next weekend.
It was all square at 9-9 at the break despite Sonny Bill Williams being dismissed 25 minutes in - the first New Zealand player to see red in 50 years - but Taulupe Faletau and Conor Murray crossed over in the second half to break their opponents' resolve.
Gatland, mocked up as a cartoon clown by the press in his homeland earlier in the tour following a round of verbal jousting, was delighted to end the back-to-back world champions' incredible eight-year unbeaten run on home turf.
"I'm a pretty happy clown this week. It's great to tie the series up and we go to Auckland next week with a series to play for," he told Sky Sports News. "Even without the red card we were the better team.
"The last 10 minutes, guys coming off their line and being aggressive impressed me. We gave away a few soft penalties but our control was pretty good.
"When we got the ball in their half we stressed them and we looked comfortably defensively. Normally when the All Black's have those kind of stats they win by 20 or 30 points. I'm proud of the performance and we can look forward to next week."
The Lions now have the chance to pull off a memorable series win when travelling to Eden Park, where the All Blacks have not lost since 1994.