Despite the Blues being victorious in their last Champions League game, their manager feels there is still more to do.
A 75th-minute goal on the counter-attack from Salomon Kalou gave Chelsea a huge advantage heading into next week's return leg at Stamford Bridge as Di Matteo's risky selection gamble paid handsome dividends.
Roberto Di Matteo. Pic/AFP
After watching Chelsea labour to a 0-0 draw at Tottenham last weekend, Di Matteo took the brave decision to omit Frank Lampard, Didier Drogba and Michael Essien from his starting line-up at the Stadium of Light.
It was the sort of decision that could have gone horribly wrong but instead Di Matteo was left to reflect on Chelsea's best away performance of the season.
However the interim coach insisted Chelsea would take nothing for granted against a Benfica side who have already helped to eliminate Manchester United from Europe this season.
"We haven't qualified yet," Di Matteo said. "It's a dangerous assumption to think you've qualified. Away from home Benfica has had some great results but we cannot think that we're through yet.
"I think we've put ourselves in a good position but it's not a result you can rely on for the home game because it's only one goal.
"You look at the results that Benfica has achieved in the Champions League and you're not going to sleep very calmly looking at that."
Nevertheless it was a far cry from the potentially fatal first leg mauling Chelsea had suffered against Napoli in the last 16, when only a miraculous comeback in the second leg saw them overturn a 3-1 deficit.
"I think we are pleased that we are in a different position going into the second leg next week," Di Matteo said.
"You know we had a mountain to climb against Napoli. Next week will be a mountain as well -- but it will be a little bit smaller because we had a good result here."
Chelsea's winning goal involved two players -- Fernando Torres and Kalou -- who had not been expected to start.
Di Matteo said with Chelsea battling in the Premier League to finish in the top four along with an FA Cup semi-final looming, his selection for Benfica had arisen out of necessity to rotate his resources.
"You know we've been playing all these games, and they're all at high intensity, and tonight was another one," he said.
"It was just a question of trying to energise the team, freshen up the team. We knew that Benfica would play at a high tempo and we needed some fresh players who could run and that was the reason for it.
"We cannot play just with 11 players. We need everybody in this squad. Players that haven't played much in the past are going to play a role in the future. It's just impossible for us to go every three days and reach fitness levels that are needed to win games."
Di Matteo also said the Portuguese connections of former Benfica duo David Luiz and Ramires, along with Paulo Ferreira and Raul Meireles had been crucial.
"One of the reasons I selected David Luiz, Meireles, Ramires and Ferreira is because they know Benfica very well, their players and the atmosphere. They've had that experience," he said.
Benfica coach Jorge Jesus meanwhile said he was confident his side could recover in the second leg.
"We still have one game to go, it will be played the same if it's 0-0," Jesus said. "We have the conviction that we weren't anything less than Chelsea. We believe we can go there and win. We didn't deserve to lose tonight."
"Chelsea had too much experience. It wasn't a just result, but the truth of the match is they won 1-0. The virtue is that they managed time very well. They were waiting for a chance and when they got their chance they scored."