Liam Craig's 69th-minute free kick proved sufficient for the visitors to return to Edinburgh with the win.
However, Jags striker Kris Doolan spurned a series of guilt-edged opportunities for the hosts and Fenlon believes that his team were lucky to emerge as victors.
He told reporters: "It was a bit of smash and grab from us if I'm totally honest.
"I thought Thistle were excellent in the first half and played really well but they probably had more chances in the second half. We were a little bit better in the second half and played better once we scored.
Hibernian have moved up to fifth in the Scottish Premier League following the victory, eight points adrift of leaders Celtic.