The German was dropped by the team after five years at the end of 2011 in favour of Nico Hulkenberg.
Sutil returned for this season and led last weekend's Australian Grand Prix.
Fernley was quick to stress that Sutil had shown this step forward even before his Melbourne drive.
"He has really looked at himself very carefully and the reasons why we took Nico as opposed to him and he has addressed them all," Fernley told AUTOSPORT. "He has answered any critics he had.
"He has the experience to deal with the pressure and we could tell when he came to Barcelona and did his first day of testing that he had got it all together."
Fernley suspects that inexperience on the 2013 Pirelli tyres thanks to completing little pre-season testing played its part in Sutil dropping to seventh later in the Melbourne race.
Sutil completed only 249 laps during testing, fewer than any of the other drivers on the Australian GP grid.
"It was probably a little bit of inexperience by Adrian on the super-softs," said Fernley.
"He tried to bring them in the right way but he hasn't quite got the technique yet.
"He's only had a few days in the car and had he had a few more races under his belt and more work on the super-softs, he could have held fifth place."
Sutil landed the Force India drive over Jules Bianchi, who also impressed in Australia on his grand prix debut for Marussia.
Fernley says that the team is aware of Bianchi's potential, but that Sutil's ability to deliver consistent points from the off tipped the decision in his favour.
"It was a tough choice that we had to make between Jules and Adrian," said Fernley.
"Jules did a super job in the race and down the road he is going to be a wonderful driver but we have to deliver and get a good result this year because next year is going to be a bit of an unknown.
"We tried to look at how Adrian would settle in and from that point of view, he has come back quickly."
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