Fernando Torres' poor performance in the semi-final first leg was explained by a stomach bug, with Demba Ba's minor hamstring injury preventing the introduction of the £7million signing from Newcastle until the final 10 minutes.
Both strikers are available against the Saints and Benitez is likely to opt for Ba in a match that Chelsea must win if the opposition to his appointment as interim boss is not to gain further traction.
Benitez was criticised for using Torres' sickness and Ba's injury as excuses for last week's cup setback, but the Spaniard said: "I was surprised the other day when I spoke about Fernando's problems with his stomach (and that) we couldn't play Demba Ba because he had a niggle.
"Afterwards it was said I was making excuses, but I wasn't making excuses.
"I am still being criticised for making the decision to play Fernando Torres instead of Demba Ba, who was a big risk if he got injured.
"If you know Demba Ba could be injured, it is my job as manager to make this decision.
"He scored two against Southampton (in the FA Cup) but couldn't play the next game against Swansea because of a niggle.
"If we can continue winning games, it's not a case of I can't win."
Benitez and chairman Bruce Buck were jeered by supporters after losing to Swansea and their anger has been only temporarily appeased by Saturday's 4-0 romp at Stoke.
Successive home defeats to QPR and Swansea, while failing to score, have heaped pressure on Chelsea to find a way through Saints' defence.
"We are doing well away but at home other teams play deep and wait and there's less space," he said.
"If we take our chances it will be totally different because the teams we play will be more open and we will have the space we're looking for.
"But if that's not the case, as in the last two games, it is more difficult.
"If a team puts 11 players behind the ball you have to find the space and be more precise."
Meanwhile, Southampton boss Nigel Adkins believes the signing of Demba Ba could see Chelsea fight for the Premier League title this season.
Adkins reckons Benitez's side remain in the title hunt.
"I think with the addition of Demba Ba now and whoever else they might bring in they look a very well-equipped side to go for the title," he said.
"It will be an interesting one but obviously he (Benitez) has started well in respect that they have won games, he is a good manager and has won the European Cup and the team play good.
"Will he win the fans around? Who knows?
"I think there has obviously been a big turnaround in managers at Chelsea anyway and I think you will find that Chelsea fans are passionate about their football club."