Richard Brittain was the match-winner with a 57th-minute effort. Fourth-placed Hibs, who now play Celtic and Hearts in successive matches in a true test of their top-six credentials, lost at home for the third time this season after a poor performance.
Fenlon said: “We didn’t play well today. We didn’t deserve to lose, but we didn’t set the right tempo from the start.
“We’re the home team. The emphasis is on us to go and win the game and I didn’t think we did that.
“We looked a little bit flat, maybe waiting for something to happen rather than going and making something happen.
“We only really reacted once they scored. That’s not good enough.”
After starting the season well, Hibs now have four points from a possible 21. Fenlon added: “We’ve stopped a little bit. Getting to the points total we got to should encourage us to see can we kick on and be better.”
Second-placed Inverness fought back twice to avert a St Stephen’s Day defeat against Clydesdale Bank Premier League opponents St Mirren. Dougie Imrie put the visitors in front in the second minute before Andrew Shinnie levelled in the 38th minute.
Stephen Thompson restored Saints’ advantage 10 minutes after half-time but Dubliner Richie Foran was on hand to save a point and a 2-2 draw for Caley in the 67th minute.
Motherwell produced a ruthless attacking display to defeat rivals Aberdeen 4-1 at Fir Park.
Kilmarnock also claimed three points with the only goal of the game in their clash with Hearts, Liam Kelly scoring from the spot on 27 minutes.
Dundee United and St Johnstone shared the spoils with a 1-1 draw.
In the Irn-Bru Third Division, Rangers enjoyed a comfortable 3-0 win over Clyde.