Diaby played just five times for Arsenal last season due to a string of injuries, including a calf problem and a broken ankle, but has started the Gunners' first three games in the new Barclays Premier League campaign.
That was enough to persuade Deschamps to pitch him straight into World Cup qualifying action and the 26-year-old repaid his faith by converting Karim Benzema's pass as Les Bleus opened their Group I campaign with a 1-0 win in Helsinki on Friday night.
And the coach, for whom it was a first competitive game in charge after succeeding Laurent Blanc, said: "He is a boy with a lot of qualities, but I knew that. He is a complete midfielder."
Diaby himself added in L'Equipe: "It was a good return, I was pleased. I hope this will be the real return."
Rio Mavuba also praised his central midfield partner, describing him as "indispensable for the France squad".
The Lille player added: "He has again proved his qualities and that he can dictate the tempo. I hope he carries on like that."
Mavuba was delighted with a winning start which he believes will be essential as France do battle with reigning world and European champions Spain in the bid to qualify for Brazil in 2014.
"It was important to start well," he said. "We are in a difficult group with Spain, who do not often slip up, so we have to win against teams like this.
"We feel this squad has a lot of scope to develop. We have to repeat the first-half performance."
Deschamps added: "It's never easy to win away from home, especially against a team who showed more than we expected.
"We controlled the game well, we were hardly ever troubled in the first half - much more so in the second when they brought on (Njazi) Kuqi.
"We did not look after the ball so well and we made some mistakes, and Finland went more direct and had more of an attacking threat.
"But we got the result. The team showed the right spirit."