Sainz admits career-best fourth was "unthinkable"

Toro Rosso driver Carlos Sainz labelled his career-best fourth place finish in the Singapore Grand Prix as "unthinkable".

Carlos Sainz Jr., Scuderia Toro Rosso STR12 and Pascal Wehrlein, Sauber C36

Esteban Ocon, Sahara Force India F1 VJM10 leads Carlos Sainz Jr., Scuderia Toro Rosso STR12

Carlos Sainz Jr., Scuderia Toro Rosso STR12, passes as Esteban Ocon, Sahara Force India F1 VJM10, emerges from the pits

Carlos Sainz Jr., Scuderia Toro Rosso STR12

The Spaniard, starting from 10th on the grid, made a poor getaway when his anti-stall kicked in, and spent a significant part of the race defending from his rivals as he opted for supersoft tyres when nearly everybody else switched to ultrasofts once the track dried up.

After the slow start, Sainz managed to slowly climb up the field and moved to fourth when Renault's Nico Hulkenberg hit trouble.

"It was a result we really earned, doing the right thing every time," said Sainz, who will drive for Renault next year. "There were complicated moments, especially when I had people with new inters behind me and mine were used.

"Then when everybody was on ultras I was on the supersofts and I had to defend very hard from people who were a second quicker than us because of the tyres.

"Then things started to happen, we passed some people and we finished fourth, which is incredible, unthinkable."

Sainz, ninth in the standings with 48 points - two more than he scored in all of 2016 - said the race had been one of the most important days of his career.

"It was a very important day. One of the most important of my sporting career and I can be very, very happy.

"It was a much harder race than you can imagine, because I had Checo [Perez] behind me with ultrasofts and Hulkenberg with fresher tyres and I spent all the race looking in the mirrors, trying not to make mistakes.

"I knew they had better pace and even so we finished ahead of them. It was much harder than it looked from the outside."

He said Toro Rosso will need to investigate the cause of the problem he had at the start.

"I don't know what happened. I'll have to analyse it because as soon as I released the clutch, the anti-stall kicked in. I don't know if it's a human error or whatever, but we'll have to analyse it.

"I stayed calm. I knew the race was very long. Once I knew I had chosen the right tyre - when they told me [Lewis] Hamilton was on it too - I had the confidence knowing that I wasn't the only one on inters."