The 26-year-old Russian rode a rollercoaster of emotions after learning he’d take over the top spot thanks to Serbian star Novak Djokovic’s quarterfinal defeat in Dubai hours earlier.

But he got the job done against Japan’s Nishioka to stay on course for a possible semifinal clash with Rafael Nadal in a rematch of the Australian Open final, which was won by the Spaniard for his record-setting 21st Grand Slam title.

Nadal — who rallied from two sets down to beat Medvedev in five sets in the Australian Open final — was scheduled to take on Tommy Paul in a later quarterfinal on Thursday.

“It’s not easy actually to play a match when you get this (news) during the day,” Medvedev said of maintaining his focus after learning he will supplant Djokovic atop the rankings on Monday.

Djokovic’s 6-4, 7-6 (7/4) upset at the hands of Czech world number 123 Jiri Vesely ensured the Serb’s reign will end.

“To be honest, I saw that he was losing, but I didn’t know that if he loses I’m going to become number one,” Medvedev said. “I thought that I had to do something big here. So then when I was receiving all the messages, well, I understood, OK, it’s gonna happen.

“The first goal for me was to still win today, because I’m here to try to win every match I play.

“But it’s definitely some great news.”

Medvedev will become the first man since 2004 outside the game’s “Big Four” of Djokovic, Nadal, Roger Federer and Andy Murray, to occupy the No 1 spot.

He becomes the third Russian man after Yevgeny Kafelnikov and Marat Safin to ascend to No 1.

Despite the distractions of the day, Medvedev needed just 70 minutes to dispatch Nishioka.

The Japanese qualifier went up an early break in the second set, but Medvedev patiently worked his way back for the win.

“He’s a tough opponent,” Medvedev said. “He knows how to return, how to run, how to make some crazy shots when you don’t expect it. I’m happy I was able to keep my composure to the end.”