Nearly two years after being fired by Inter Milan, Benitez took over as interim Chelsea coach on Wednesday following the European champions' abrupt dismissal of Roberto Di Matteo.
The Spaniard's first chance of a trophy will come at next month's Club World Cup, which Benitez won at Inter days before a six-month stint with the Italian club was ended.
"Benitez has been trying to get a job for a long time and he is very lucky because on his CV in two weeks' time he could have two world club titles to his name — and had nothing to do with the teams," said Ferguson, who has been in charge of Manchester United for 26 years.
The pair often clashed during Benitez's time at Liverpool from 2004-10, with their most spectacular conflict coming in 2009 when Ferguson suggested Liverpool would be affected by nerves late in the Premier League title chase.
Benitez retorted by reading out a hand-written list of "facts" to back up his claim that Ferguson wasn't punished enough for verbally using referees and match officials.
Benitez came out of his stint at Liverpool with a reputation as one of the best managers in Europe, winning the Champions League in 2005 and reaching the final in '07. He had previously broken the duopoly of Barcelona and Real Madrid in Spain by winning the domestic title twice in three years with Valencia, as well as capturing the UEFA Cup.
At Inter, though, Benitez's standing took a hit.
"Jose Mourinho won the treble at Inter. Rafa took over and they won the world title without having to do anything," Ferguson said. "He had nothing to do with the construction of the team."
Despite his ongoing feud with Benitez, Ferguson said he hopes the Spaniard enjoys a good start to his reign at Chelsea — because the team's first game is Sunday against Manchester City, the Premier League leader and arguably United's biggest title rival again this season.
"I hope he is lucky on Sunday, too," Ferguson said. "It happens time and time again when a new manager comes in that a team win their first few games.
"It is strange how it happens and sometimes you wonder if it encourages chairmen at football clubs to make changes because they think, 'If we get a new manager we'll win the next two or three games.'"