Cristiano Ronaldo celebrated the signing of his new contract with Real Madrid in stunning fashion with his 23rd career hat-trick as the Spanish giants hammered Galatasaray 6-1 at the Turk Telekom Arena on Tuesday.

The Turkish champions had beaten Madrid on their visit to Istanbul in last season's quarter-finals and started the brighter of the two sides with Felipe Melo seeing a trio of efforts saved.

However, the Spanish giants were rarely troubled after Isco had fired them into the lead 12 minutes before half-time as they cruised to victory in the second half thanks to two goals from Karim Benzema and three from Ronaldo.

Umut Bulut's late strike was the only consolation for the hosts.

"We couldn't have started better. To start in this manner gives us a lot of confidence," Ronaldo told Spanish TVE afterwards.

"We did our job against a very complicated opponent. Despite the result it was a difficult game.

"In the first few minutes they had their best chances. After our first goal we controlled the game and played well."

Real boss Carlo Ancelotti made Gareth Bale wait to make his European debut with the nine-time winners as he started on the bench before coming on for the final half-hour.

However, it wasn't a happy evening for captain Iker Casillas as he had to be withdrawn just 15 minutes into his first appearance for the club in eight months due to a rib injury.

The Spanish international collided with teammate Sergio Ramos after just 60 seconds as he collected a routine cross into the area and, despite making one flying save from Melo, was in some discomfort as he came off to be replaced by Diego Lopez.

"He has been unlucky because the got a knock from Ramos. He showed in the few minutes he was on the field he is in good condition and he made a very good save," said Ancelotti.

"I have spoken with him and he is not too worried so we hope it is just a knock and he will be fine in a few days."

The game was turned decisively in Madrid's favour when Isco controlled Angel di Maria's pass wonderfully before dispatching the ball into the net via the inside of the post just after the half hour mark, but Ancelotti admitted his side hadn't been at their best in the opening period.

"The result makes the game look easy but it was anything but in the first-half. We had a lot of problems and had to survive a lot of pressure.

"After the first goal by Isco it is true that things became easier, we were abe to use the counter-attack more and when Cristiano and Benzema have space they are very dangerous."

Galatasaray should have levelled early in the second period when Burak Yilmaz somehow headed wide from Nourredine Amrabat's cross.

However, within minutes the floodgates had opened as Di Maria slid in Benzema to slot home his third goal of the season.

Ronaldo was the competition's top scorer last season with 12 and he finally got in on the act with two goals in little over three minutes just after the hour mark.

The Portuguese fired high into the net from point-blank range from Isco's headed cut-back and then volleyed home after Fernando Muslera could only parry Sergio Ramos' header from Bale's free-kick.

Ronaldo also played a key role in Madrid's fifth as he squared for Benzema to tap home his second of the evening from close range before Bulut restored some pride for the hosts with a deft finish of his own from Amrabat's cross.

And, fittingly, it was Ronaldo who was to have the final say with an incredible individual effort in stoppage time as he weaved past three Galatasaray defenders before smashing the ball high past the helpless Muslera.