See Alex de Minaur's touching gesture for girlfriend Katie Boulter after the Aussie's big French Open win was hit by controversy

Aussie tennis star Alex de Minaur has savoured his best win on the Roland Garros clay before racing over to girlfriend Katie Boulter's late-night match to cheer her on.

The Australian No.1 and his young American hot-shot opponent Alex Michelsen had to hang around for an age, including a false start when they actually came on to Court Simmone Mathieu and were dragged off again before even getting the chance to warm up.

But when they finally did get going on Tuesday, with de Minaur wearing a thermal undershirt to keep out the cold on the damp, miserable day, he still lit up Roland Garros's most beautiful 'garden' court with his 6-1 6-0 6-2 demolition job on the 19-year-old who had blitzed him on a hard court in Los Cabos in April.

'The Demon' was then spotted shortly afterwards at girlfriend Katie Boulter's night match on Court 9, where she was facing Paula Badosa.

A photo of him fist pumping his encouragement appeared on social media, with the post also noting that Badosa's boyfriend Stefanos Tsitsipas was not in attendance.

De Minaur's match had its own controversial moments, with his teenage opponent throwing a tantrum over an umpire's decision that drew whistles from the crowd.

Michelsen reacted to a line call by screaming at the umpire, 'Oh my god! Oh my god! Oh my god! that is the least funny thing I've ever heard in my entire life!' with the outburst slammed by tennis fans. 

And though he's too nice a guy to revel in it, de Minaur couldn't hide his satisfaction that revenge was a dish best served up cold - and wet.

'I wasn't easy out there today. Obviously a long day, stop, starting. More than anything mentally, having to deal with cold and rain in your face. Just had to make sure I had good mentality today. That's probably the most important thing.

'I feel like every time I come here to Paris, it's raining. I can remember very few times where I feel like I've played a hot day here, and I remember plenty of these types of matches, sadly.

'But I knew what to expect. I was ready. I had my undershirt thermal layering on. Yeah, I was ready for a battle in the cold and rain.'

Much more ready than his young opponent, who looked thoroughly disenchanted with the clay, the rain, de Minaur's killer drop shots and, last but not least, an umpire who he berated wildly for one bad call as if he were a Supermac de nos jours.

When asked about his defeat by Michelsen in Mexico, de Minaur chose his words carefully.

'That match I'd flown from Rotterdam basically the night before from an indoor event to an outdoor event in Mexico. It was quite a quick turnaround. So I probably wasn't quite ready to play -- but I definitely was ready today.'

His performance was dotted with some virtuoso shotmaking and de Minaur, who next meets tough Spanish clay-courter Jaume Munar, was most pleased with the way he handed the testing, heavy conditions by looking on the bright side of life.

'The most important thing was to have a positive mindset throughout the whole day because it's very easy to start complaining about the weather, the conditions, everything, but if you start down that rabbit hole, you can probably guarantee you're not going to play a good-level match.

'So you've got to take it lightly. You've got to see the bright side of it. Even though it's a little bit fake it until you make it, right?

'I was telling myself walking into the match that 'I love these types of conditions, you know I wish every day was like this'.

After the way he played, perhaps he really does wish that now.