Roger Federer's unbeaten start to 2018 remained intact at Indian Wells, but only just.

The Swiss, who won the Australian Open in January to move to 20 Grand Slam crowns in total, edged past Berna Coric in three sets to progress to yet another final.

Having lost the first set, the 36-year-old recovered to win 5-7 6-4 6-4, sealing his place against Juan Martin Del Potro in the last two of the BNP Paribas Open.

Federer is 17 games unbeaten, and while Del Potro will relish the challenge that awaits him in the final, very few would be able to live with him in this kind of form.

He reclaimed his world number one spot last month too from Rafael Nadal, becoming the oldest player in tennis history to do so, and the last 14 months or so have been remarkable for a man written off because of his age.

It's almost a throwback to a decade ago with Nadal and the Swiss dominating the Grand Slams, sharing the last five between them, and it has been a fascinating duel while Novak Djokovic and Andy Murray have been injured.

But in typically honest style, Federer admitted he was far from happy with his performance against Coric.

He even claimed he was lucky to get past the Croat in the first Masters 1000 event of the season, and that it was his hardest match of the season so far.

Federer's record against the Argentine will give him confidence though, winning three of their last four meetings, but he was adamant that he shouldn't even have the chance to play him.

"I should have lost the match," Federer stated. "I was down a break twice in the third, down a break in the second.

"This is the toughest I’ve been pushed this year, more than the Australian Open final.

"It is another chance for a title and that would be amazing. But I don’t expect it.

"I am just happy that I am injury free and playing as well as I am.

"To be winning the matches through fight and grit is a great feeling."

Brilliant honesty from Federer, though that's not likely to make Coric feel any better after surrendering his one set lead yesterday.

But as they say, winning when you don't deserve to is the mark of a true champion.

And that's exactly what Federer is.