A goal in either half from Leigh Griffiths gave them a two-goal lead, but the Edinburgh side had to withstand a fightback from Saints, who couldn't add to Steven Thompson's goal.
However, the hosts were perhaps made to rue their penalty miss, with Paul McGowan's first-half spot-kick saved by Hibernian keeper Ben Williams.
But Fenlon thought his side deserved the victory because of their strong first-half performance.
"I was delighted with the performance especially in the first half when we passed the ball well," said the Hibs boss.
"Saints changed their shape in the second half but I then thought we defended well. And at the other end Griffiths and Eoin Doyle are forming a good partnership and always looked a threat."
Hibs have produced two good performances since their opening day 3-0 hammering by Dundee United.
Fenlon added: "Sometimes a manger has to accept the responsibility of the tactics being wrong and I think I got it wrong at Tannadice.
"After losing heavily in the (Scottish) Cup final (against Hearts last season) and then losing by three to Dundee United the players have shown tremendous character in their last two games."
Danny Lennon was disappointed to see St Mirren lose for the first time and give up their top of the table spot.
But Lennon was more concerned with the injury to Darren McGregor. The early indication is that the defender, having already recovered from a cruciate knee injury, has similarly damaged the other knee but the Saints boss is confident that he will fight back again.
"It is not looking too good for Darren, who had a tremendous fightback from injury last season," confessed Lennon.
"I wasn't sure when it happened and I thought at first it was a head injury. But with the backing of our great medical team and his character I'm sure he will come though it."
The Saints boss was disappointed with his team's first-half performance not helped by McGowan's penalty miss.
Lennon, though, preferred to criticise the entire team, saying: "I thought the side was unrecognisable in the first half. When we don't have our passing game we play deeper and Hibs took full advantage.
"We changed things in the second half I couldn't have asked for any more except maybe another goal. Dougie Imrie and Gary Teale provided lost of crosses and I felt Steven Thompson and Sam Parkin gave them a handful.
"The second half was much more pleasing and we have to credit the fans who got right behind us."