Juan Martin del Potro should not yet be in any condition to defeat elite tennis players. This is clear. It was made clear long before he stepped out to court in Madrid, when the opening days of his comeback featured straightforward losses to the likes of Guido Pella and Horacio Zeballos on hard courts. His previously imperious conviction was replaced with the hesitance and tentativeness naturally borne out of two years absent from the tour. It was also made clear in Madrid on Tuesday, when his increased conviction still only allowed him to float over feathery two-handed backhands void of spin and ripe for destruction. And it was made clear after the fact by del Potro himself.

“I believe in myself all the time,” he said after his 7-6 6-4 victory over Dominic Thiem. “But (even) when I won the first set I thought I couldn't win this match. He's playing really well this season. He's playing great on clay courts. That's why I'm surprised with my level too.”

The question that elicited del Potro’s honest response asked him at which point he believed he could win the match. Although he couldn’t consciously specify any moment he believed he could defeat the hottest young player in men’s tennis, the moment it occurred was clear. Serving up 7-6 3-2 - a lead he built and maintained by serving well enough and determinedly defending in longer rallies that were all invariably played to his recovering backhand - he reached the tipping point as the previously dire Thiem awoke to flash three winners and find a break point.

Only certain players are seemingly innately equipped to sense the rhythms and momentum of a match and to adapt to them in an instant. The previous set and a half may have suggested that consistency in the face of an inconsistent opponent was the likeliest route to success for a del Potro lacking so many of his weapons. But although Del Potro hasn’t played many matches over the past two years, his credentials are undeniable. When he arrived at this crossroads, he didn’t hesitate to depart from the tennis that brought him to that lead. He saved the break point with a destructive service winner. He followed it up by forcing an error with a trademark destructive crosscourt forehand. Then he stepped further into the court, pairing another nuclear forehand with a drop shot.

In three points, Del Potro took control of the match and slammed the door shut. From that point onward, he was standing on the baseline where all 6ft6 tennis players should stand. He followed the scuppering of Thiem’s break point with a love hold. And although nerves in the face of victory arrived in the final game, he had the wherewithal to see out the victory, a victory that reduced him to sobbing in a towel.

“I think that today I have a lot of joy. I'm very happy. It's because some great things are happening to me right now. I wasn't crying because I had to leave or because my wrist was hurting or anything. I was just very happy about it.”

Del Potro may have been emotional after his victory, as one would expect both in the context of such a step forward and considering his tendency to shed buckets of tears. But it was the sobriety toward his goals ahead that was more significant.

“I cannot pretend to get a new trainer because I'm still spending a lot of time doing exercises with my wrist,” he said. “If I'm closer to achieving my goals, of course I would like to think about a new team as soon as possible, and a good, strong team.”

“I think I improved a lot since my last match in Munich. Today, I hit it really well. I'm growing up with my backhand. I'm getting confidence with my backhand too.”

Del Potro understood that the most significant victory in this match wasn’t the victory in itself but the mere, novel concept of being able to grasp the racquet with two hands and hit somewhat proper backhands throughout the match without anything happening to his wrist, and without fear of what could possibly happen to it. The victory was in being able to maintain his full focus on the match, and only the match.

“I think I believe on the way that I'm working now, and that's what I have to do to get better in the future. I'm getting closer every day, but still I'm very far away from my highest level,” he admitted.

Overall, in spite of the tears, del Potro was aware that this is only one step forward in what he hopes will eventually evolve into a steady march. It may be that he is able to replicate the success of today and continue moving forward, or that his match tomorrow against Jack Sock will prove a step too far. But regardless, today’s clear step will undoubtedly give him more hope that the condition of his game or of his wrist won’t be a question for so much longer.