While Alex de Minaur looks more comfortable and impressive on the clay with every passing match, the great Novak Djokovic seems to be losing his magical powers on the red stuff.

For while Australia's No.1 kicked off his Madrid Open quest with a clinical 6-2 6-3 victory over Italian Lorenzo Sonego on Saturday, all the talk at the Caja Magica surrounded another dismal first-round defeat for Djokovic, whose quest for 100 titles took another savage hit.

Australia's No.1 de Minaur made just nine unforced errors in a clinical, almost Djokovic-like dismantling of Sonego, before the mighty Serb, almost unthinkably, then went out and lost his third match in a row, succumbing tamely to incredulous Italian Matteo Arnaldi 6-3 6-4.

It was such a disappointing defeat for the 37-year-old Djokovic that he even pondered afterwards whether he would be back next year, a sure sign he's concerned his powers really are on the decline.

De Minaur's clay-court prowess, though, is clearly only on the up. "Como en casa" he scrawled on the camera lens after his 75-minute lesson to Sonego. In other words, the clay courts feel just like home to the Spanish-based Aussie at the moment.

The world No.7 reached the semi-final in Monte Carlo and the quarters in Barcelona, and admits he now feels completely different on the clay this year, full of confidence on a surface that once tormented him.

The 26-year-old is now looking at the prospect of a big run in the Masters 1000 event at altitude on the faster Madrid courts to set him on his way to Roland Garros.

"I was very happy with how I settled mentally, and was able to bounce back straight back after losing my serve first game and I really ended up playing some great tennis. So very happy with that."

"The thing that's been helping me out the most has been the serve. Today was a great serving day for me, and it made my life a lot easier," added the Aussie, who next faces Denis Shapovalov in the third round after the Canadian southpaw outplayed Kei Nishikori 6-1 6-4.

Asked about his striking general clay-court improvement, de Minaur added: "You see less unforced errors from me, and at the same time, you see me being a little bit more aggressive, able to hurt my opponents in different ways."

For Djokovic, though, the old assuredness has - for now at least - deserted him after he followed up his Miami Open final defeat and Monte Carlo Masters first-round loss with another sub-par outing, littered with 32 unforced errors.

"I've had a few of these this year where I lose in the first round, unfortunately," sighed Djokovic.

"Still my level of tennis is not where I would like it to be."

Asked if he'd just played his last match in Madrid, Djokovic said: "It could be, it could be. I'm not sure if I will come back. So, I don't know, I don't know what to say.

"I mean, I'll come back, maybe not as a player. I hope it's not, but it could be."

For world No.44 Arnaldi, though, beating his idol was a dream result. His message on the camera lens read simply: "OMG" - 'Oh, my god'.

Elsewhere, Stefanos Tsitsipas fought back against Jan-Lennard Struff 3-6 6-4 6-3 and will face 10th-seeded Loranzo Musetti, who beat Tomas Martin Etcheverry 7-6 (7-3) 6-2.