With a stalemate looming and the visiting fans' ire for Benitez and Torres increasing, Oscar came off the bench to score the winner eight minutes from time to give last season's Champions League winners the advantage ahead of next week's second leg of the last-32 tie at Stamford Bridge.
"Eighteen attempts away is not bad, but we have to be more clinical in attack," Benitez said. "The first 20 minutes we were in control. We had some half-chances; it was a cross, we weren't there. We were in control.
"After this 20 minutes they were pushing and pushing. The team, as a team, had problems defending.
"We changed a little bit in the second half. I think the concentration of the team was much better, the intensity in defence was much better and then we had more control."
Many of the missed opportunities fell to Torres, a £50million striker who now has one goal in 13 games.
Torres missed a straightforward effort after 35 minutes when teed up by Juan Mata and sliced a second-half shot out for a throw-in in another impotent display at the Generali Arena.
Benitez, who managed Torres at Liverpool, refused to criticise his compatriot, even though the World Cup winner did not make an effort to meet two early crosses from Eden Hazard and looked disinterested at times.
"We have to create more opportunities and the strikers will score more goals," Benitez said.
"His work rate was really good and thanks to him the rest of the team, especially the second line of offensive players, they could create.
"His job was to push and run and keep their defenders deep so he could create space for the other players.
"Everybody expects from a striker just to score goals, but he's doing also a great job for the team."
Captain John Terry travelled to Prague after missing last Saturday's 4-1 Barclays Premier League defeat of Wigan with inflammation of his knee, but was kept on the bench.
Ashley Cole was also an unused substitute, due to a cold and Benitez's wish to give Ryan Bertrand an opportunity.
Branislav Ivanovic and Gary Cahill played in central defence as the Blues recorded back-to-back wins for the first time since December and kept a clean sheet for a second time in eight games.
Terry, who has started just twice under Benitez, who was appointed in November, may yet return for Sunday's FA Cup fourth round replay with Brentford.
"He had a setback," Benitez said. "After he was fine again. He had no reaction in the next training session.
"It's a vicious circle: if he cannot play, he cannot improve his match fitness. We have to manage.
"In the meantime if Cahill and Ivanovic are doing well at least we can keep winning games."
After ending Sparta's 11-match unbeaten home run in Europe, Benitez is now optimistic of progressing to a last 16 tie against Ajax or Steaua Bucharest.
"We have scored the away goal and we have to finish the job at home," he said. "We know it will not be easy."
Chelsea were playing in the Europa League for the first time since 2002 and at times appeared reluctant to partake in the second-rank European competition.
Benitez said: "That is the competition that we have to play now. It's a European competition and they (the players) have to realise it's an opportunity to win a trophy.
"I'm sure if we can progress they will see the option and hopefully we can keep the team playing well and winning games, until the end (final)."
Sparta coach Vitezslav Lavicka felt Chelsea were ruthless in the end in his side's first competitive match since December 6.
"From the 60th minute we were under pressure," Lavicka said. "We lost balls when we were attacking. Then the opponent had the chances.
"Unfortunately we didn't have the energy and the opponent punished us with the goal they scored.
"It was a factor, but it's not an excuse for us. In the Czech Republic we have a winter break and that's what we have to deal with.
"We tried to prepare as best we could but the opponent was still very strong."