Torres and Luiz both beat the 11pm cut-off to join the Barclays Premier League champions.
Striker Torres arrived for a reported £50million from Liverpool, smashing the transfer record between British clubs, while Benfica finally allowed defender Luiz to move on in a £25million-plus deal.
After signing a five-and-a-half-year contract at Stamford Bridge, Spain striker Torres told his new club's official website: "I am very happy with my transfer to Chelsea and I am looking forward very much to helping my new team-mates this season and for many years to come.
"Having played against Chelsea many times since coming to England, and in some very big games I will never forget, I know there are many great players here and I will work hard to win a place in the team.
"I hope I can score some important goals for the supporters to enjoy this season."
Chelsea chairman Bruce Buck said: "This is a very significant day for Chelsea, capturing one of the best players in the world with his peak years ahead of him.
"We have long admired the talents of a player who is a proven goalscorer in English football and Fernando's arrival is a sign of our continuing high ambitious. I hope every Chelsea fan is as excited as I am with this news."
Brazil centre back Luiz joins from Benfica for a fee of 25 million euros and Chelsea's Serbian midfielder Nemanja Matic will move to Benfica as part of the deal.
Luiz, 23, had a contract with Benfica that ran until 2015 and is seen as one of the most promising defenders in Europe.
He arrived in Lisbon from Brazil in 2007 and was a key member of the Benfica side that last season clinched the Portuguese Premier League title for the first time in five years, missing only one of 30 league matches.
His performances earned him a debut call-up to the Brazil squad for a friendly against the United States in August. He also played against Iran and Ukraine in October and is in the squad for the February 9 friendly in France.