After Alonso announced he would be retiring from Formula 1 at the end of the year, McLaren have moved quickly to snap up his successor and Sainz will join on a multi-year contract.
The highly-rated Sainz has been on loan at Renault from Red Bull this season, but was available for 2019 after the French team successfully pursued Daniel Ricciardo to partner Nico Hulkenberg.
“We’re incredibly excited to have Carlos join us as a McLaren driver,” said McLaren CEO Zak Brown. “We’ve been assessing him for some time now and rate him very highly among the next generation of young talent emerging through the ranks in Formula 1.
“Carlos brings with him the perfect blend of youth and experience. Although he’s just 23, he’ll be starting his fifth season in the sport with us and will bring with him a huge amount of racing experience, both in Formula 1 and with our partner Renault.”
Sainz added: “I’m delighted to finally be able to confirm that I’ll be a McLaren driver from the 2019 season. It’s something I’ve been looking at for a while and I’m very excited about this next chapter in my career.
“I’ve been a McLaren fan for as long as I can remember. It’s a great name in the sport with an incredible heritage, and the list of drivers that have raced for McLaren over the years are among the heroes of Formula 1.
“Fernando is of course one of them, so it’s particularly special that I’ll be taking his seat as part of the next generation of Spanish racing drivers behind the wheel of a McLaren.”
It is not yet clear who will be Sainz’s team-mate at McLaren next season, though Stoffel Vandoorne and Lando Norris are the clear frontrunners for the seat.
The natural favourite would be current driver Vandoorne, but the Belgian has failed to live up to expectations during his two years in F1 with the Woking team and has yet to out-qualify Alonso this season.
British teenager Norris, meanwhile, a McLaren young driver, is enjoying an impressive rookie campaign in F2.
McLaren said they would announce their full driver line-up for the 2019 season “in due course”.
Sainz’s move to McLaren also opens the door for Pierre Gasly to step up to Red Bull for 2019 and partner Max Verstappen.
Team boss Christian Horner said he would be looking to youth to fill the void left by Ricciardo, and Gasly has shone in his first full F1 season with Toro Rosso.
What does Sainz’s move mean for transfer market?
McLaren chief Brown claims he knew of Alonso’s decision months before his announcement, and so had been speaking to drivers “up and down the grid” about replacing the two-time world champion.
Sainz and Ricciardo were two of the leading contenders, but after the Australian turned down McLaren in favour of a shock move to Renault, Brown had one driver in his sights – the Spanish compatriot and friend of Alonso.
“It’s no secret that Carlos is a huge admirer of Fernando’s, and it’s fitting that he will be stepping into his seat as a Spaniard with a legendary name in motorsport,” he said.
“We think he’ll be a great fit for McLaren and we’re really excited to have him join us from next season and beyond.”
Ricciardo’s departure from Red Bull could have made negotiations trickier – Sainz, well-respected at Red Bull, and Gasly were considered frontrunners for the seat.
But perhaps Sainz’s fractured relationship with Verstappen during their time at Toro Rosso counted against him, and it now looks likely that Gasly will partner the Dutchman as team boss Christian Horner looks to promote from within.
Gasly’s exit would, however, leave a seat open at Toro Rosso, which could be filled by British youngster Dan Ticktum – providing he gets enough license points – or even McLaren youngster Norris.
The F2 frontrunner is a leading contender to team up with Sainz for 2019, along with Vandoorne, but even if Norris is not successful, McLaren would still love for him to be in F1 next season.
Time for Sainz to live up to his potential?
Sainz, the son of the decorated World Rally champion of the same name, entered Formula 1 with Toro Rosso in 2015, along with Verstappen.
As such, comparisons between the two young drivers were inevitable.
Despite being heavily out-scored by Verstappen in their only season together, Sainz had several more reliability failures and stacked up favourably against the Dutchman in qualifying.
There were, however, several clashes both on and off the track and it never looked to be a viable partnership going forward.
Verstappen was promoted to Red Bull early into 2016 but Sainz, adamant that he deserved the call-up, continued to enhance his reputation as one of the sport’s hottest young talents.
There were several fine drives over his three years with Toro Rosso: his fourth place in Singapore last year the pick of the bunch.
But with Red Bull’s stable of Verstappen and Ricciardo seemingly long-term, Sainz agitated for a move away from the junior team and signed for Renault on loan towards the end of the 2017 season.
Sainz understandably struggled at the start of his Renault career against an experienced and remarkably consistent driver in Hulkenberg but has improved in recent months and his fifth-place finish for the team in Baku deserves huge credit.
However, Ricciardo’s availability proved too tempting to resist for Renault – they were previously courting Esteban Ocon – and it meant Sainz was essentially on the market for 2019, providing Red Bull didn’t want him for the senior team.
It seems they have opted for Gasly instead, and Sainz will now want to prove to both Red Bull and Renault that they were wrong to snub him.
Can McLaren get the most out of his undoubted talent?
F1 will be back from its summer break with the Belgian GP, live on Sky Sports F1. The race begins at 2.10pm on Sunday, August 26. Get Sky Sports F1 – the home of every race weekend LIVE in 2018.
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