Federer will reclaim the top spot after a record gap of five years and 106 days when rankings are updated on Monday.
At age 36, he will overtake Andre Agassi as the oldest No. 1 by three years.
He will also extend his record for total weeks at the peak to 303.
But surely even more remarkable will be the record gap of 14 years and 17 days between the time he first became world No. 1 and his latest return.
The previous best for that mark is nine years and 184 days by incumbent and great career rival Rafael Nadal.
To be able to be the top player in his sport across that unprecedented time span — when combined with his record 20 grand slam titles earned between 2003 and 2018 — illustrates the true greatness of a player considered the best of all time.
Playing his first tournament since claiming his sixth Australian Open title, Federer moved within touching distance one of the No. 1 spot with a 7-6 (10-8) 7-5 defeat of fellow veteran Philipp Kohlschreiber in the second round in Rotterdam, to set up the quarter-final clash with Haase.
"Tonight was complicated, I had to fight and struggle," Federer said. "I had a good game plan going in, but I was never able to completely pull it off.
"This is an exciting challenge, I've struggled to try and get there. I had to win a lot of matches last year.
"I never imagined this after my (February 2016) knee surgery. Number one is a tough place to get to."
Since breaking down again at Wimbledon in 2016, Federer has won eight titles, including three grand slams, while winning 61 matches and suffering just five defeats.
"I would have had great regrets if I had not come here this week," Federer said. "I'm very excited for tomorrow's match, I can't wait for it to come around."
FEDERER'S NEW HISTORY
Total weeks as world No. 1: 1 Roger Federer 303 2 Pete Sampras 286 3 Ivan Lendl 270
Oldest No. 1s in men's rankings history: 1 Roger Federer, 36, on 19 February 2018 2 Andre Agassi, 33, on 7 September 2003 3 Rafael Nadal, 31, on 18 February 2018
Longest Gap Between Stints as No. 1: 1 Roger Federer 5 years, 106 days 2 Andre Agassi 3 years, 142 days (1996-99) 3 Jimmy Connors 3 years, 65 days
Longest Gap Between first and most recent day as No. 1: 1 Roger Federer 14 years, 17 days 2 Rafael Nadal 9 years, 184 days 3 Jimmy Connors 8 years, 339 days.
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