Demba Ba got life at Chelsea off to a fine start Saturday, scoring twice in his debut as the FA Cup holders secured safe passage to the fourth round at the expense of Southampton.
The 27-year-old Ba completed his move from Newcastle to West London on Friday and took just 35 minutes to open his account for the Blues.
Ba put the tie out of any doubt in the 61st minute, linking up impressively with his new teammates to slot home past Artur Boruc.
The Senegal international was denied a hat-trick goal by the Southampton goalkeeper, who was beaten from the penalty spot by Frank Lampard, who equaled Kerry Dixon's all-mark of 193 for Chelsea to put him joint second behind Bobby Tambling.
The match took a while to get going on a mild afternoon at St Mary's, with David Luiz's tame 13th-minute effort the first of note.
"It is a great achievement for him and hopefully he can score a lot of goals until the end of the season," Benitez said. "We will be happy and he will be happy if that happens."
Ba's display was so impressive that Fernando Torres, a player rejuvenated under Benitez, was left on the bench at St Mary's.
"I prefer this problem than just to have just one," Benitez said when asked if the pair will prove a selection headache. "It is important for the team to have these different options, good players. They can compete or they can play together, depending on the game. They can play together I think. He was playing at Newcastle with Papiss Cisse and can do it because he is a clever player."
Play swung from end to end as both sides patiently waited for an opener, which went to the home side.
The 22nd-minute strike jolted the visitors into life and Eden Hazard soon came close with a curled effort that went narrowly wide of the far post.
Luiz had to react quickly to deny James Ward-Prowse at the other end after the teenager found space on the edge of the box, but the Blues were becoming an increasing attacking threat.
Ba's link-up play was improving as the half wore on and Saints were having to defend resolutely.
However, their resistance only lasted 35 minutes as the new boy opened his Chelsea account. Hazard played through Mata, whose dink over Boruc was creeping in only for Ba to fire into the roof of the net.
Boruc was almost beaten again four minutes later, but his spill from a Moses strike went wide.
The Polish goalkeeper was looking rusty on what was only his second start since Oct. 28 and soon fumbled a long-range Cesar Azpilicueta strike.
Chelsea was playing with new-found confidence and took the lead in first-half stoppage time, with Moses collecting a cutback from Ashley Cole to power home a low left-footed strike.
The Blues continued in the ascendancy after the restart, with Mata seeing a strike deflected wide by Guly do Prado shortly after the restart.
The Spaniard was involved yet again in the 52nd minute, sending over a left wing cross that Ivanovic headed home at the near post.
Only an excellent tackle from Luke Shaw prevented Hazard getting a fourth shortly afterwards, although Chelsea soon found the back of the net.
Having started the move, Ba showed excellent movement to latch onto a Hazard pass from the right to slot home under pressure from captain Jose Fonte.
The Portuguese defender looked to be badly injured in the challenge and was stretchered off, with Jos Hooiveld coming on in his place.
A great double save denied first substitute Steve de Ridder and then Steven Davis as Saints looked to claw a goal back, before Ba was denied a hat-trick by Boruc.
The Saints goalkeeper did excellently to stop the striker's header with his feet and had to be alert to deny substitute Lampard.
However, the midfielder did get on the scoresheet seven minutes from time.
Davis was harshly judged to have handled and the 34-year-old sent Boruc the wrong way to equal Tambling's record of 25 FA Cup goals for Chelsea.
"The first half we had to work but after that little by little the team was getting better," Benitez said. "The second half was much better. We played with quality and when you're one goal ahead they have to take more risks." Information from Press Association was used in this report.