Everton manager Roberto Martinez hailed Leighton Baines' new contract as the club's biggest possible January signing.
The England international has signed a new four-year deal which the Toffees boss believes will see the club benefit from the left-back's best years of his career.
Baines, 29, had been a target for former manager David Moyes at Manchester United, who had two bids rejected in the summer, but Martinez has persuaded him to extend his stay at Goodison Park - providing a significant boost on the eve of the 222nd Merseyside derby at Anfield.
"It is an important moment for us," said Martinez.
"You are talking about January signings and bringing players into the club but no-one will be bigger than having Leighton Baines focusing on being as good as he can be for Everton in the best years of his career.
"There were going to be a lot of clubs fighting for those years (of Leighton's career).
"He has a World Cup around the corner and you see what a consistent performer he is - not many players can play 38 league games two seasons out of the last three.
"He has been performing as one the best left-backs in European football and the best is yet to come because now he is in a position where he can enjoy the experience and understanding of the game and affect others around you.
"You look at how important he is with the daily standards, the influence he has with the younger players.
"I am just looking what Leighton can do in the next four years in the dressing room and it is going to be as good as it gets."
The timing of the news may well have been stage-managed by Everton as they head to Anfield looking for their first league win this century.
However, the implications of Baines committing himself to the club are far-reaching as it shows the confidence a player desperate to play Champions League football has in his manager.
Martinez succeeded Moyes in the summer and has brought an attacking style of football to the team without any drop in performance and they head into Tuesday's match just a point behind their near-neighbours, whose manager Brendan Rodgers still talks about them as being title contenders.
"It represents a strong intent of trying to progress and get stronger and Leighton will bring that on the football pitch," added the Toffees boss.
"It is a great boost internally but I know fans will be delighted because Leighton is more than a footballer at the club.
"You look how important he is with the daily standards, the influence he has with the younger players.
"I am just looking what Leighton can do in the next four years in the dressing room and it is going to be as good as it gets.
"To have Leighton with the focus and tranquillity to be at Everton for the long-term is an incredible boost."
Everton have not won at Anfield since Kevin Campbell scored the only goal in September 1999.
It is a psychological hurdle which needs to be overcome but having ended a 21-year wait for a victory at Old Trafford last month, Martinez sees no reason why they cannot repeat the feat at Anfield.
"This season we've had a couple of big experiences in that respect There is a mental battle you have to overcome," he added.
"You can come down to the tactical and technical aspects of any performance but more importantly psychologically you have to have that winning mentality.
"This season we have been tested in that respect: going to the Emirates and being able to perform how we did (drawing 1-1) and going to Old Trafford and winning after 21 years means as a group we are ready to go anywhere and be ourselves."
A delighted Baines admitted he could not be happier to be staying at Everton - and is similarly pleased the new contract will put an end to speculation about his future.
He told evertonfc.com: "I am delighted to have agreed the new deal.
"I am very happy at Everton and always have been. It's a fantastic football club and I am excited about what we can achieve here in the next few years.
"I've loved every minute of being here since I first joined in 2007 and I couldn't be happier."
Baines insisted all the transfer talk had not affected his performances, but is nevertheless happy to see an end to it.
"Was it a distraction? Not for me, no," he said.
"I am a professional footballer and speculation is part and parcel of the industry we are in but it never affected me for a moment on the pitch.
"Of course it was on my mind at times away from pitch because I was getting asked about it everywhere I went but I hope the supporters could see that I didn't let it affect me at all once I crossed the white line.
"I've never been one to relish the limelight so I suppose I'm glad that the speculation will go away now."