Fourteen years after first grabbing the number one ranking, the 36-year-old Swiss maestro is back on top of the world, the oldest man to achieve such a feat in the sport's history.
It is Roger Federer's first time back at the summit since October 2012 having first claimed the top position in February 2004.
An irritated world number one Caroline Wozniacki progressed to the Qatar Open quarter-finals on Thursday in a feisty match where she complained and apparently mocked her opponent Monica Niculescu's grunting.
Roger Federer would surpass Andre Agassi, who held the top spot in 2003 aged 33 years and 131 days. It would be Federer's first time back at the summit since October 2012 having first claimed the top spot in February 2004.
Garbine Muguruza is set to take on either Frenchwoman Caroline Garcia, the seventh seed, or Russian qualifier Anna Blinkova for a place in the semi-finals.
World number two Simona Halep won on her return to competitive action since losing the Australian Open final, beating Ekaterina Makarova in straight sets in the Qatar Open on Wednesday.
Second seed Dimitrov had to fight back in the second set to defeat Japan's Yuichi Sugita 6-4, 7-6 (7/5) in their first-round encounter.
Sania, regarded as India's best-ever women's tennis player, has achieved at least one medal at every Asiad meet since 2006.
The ATP Tour officials say they are reviewing "allegations of racial prejudice" after Ryan Harrison and Donald Young exchanged words in the first set and had to be separated by the chair umpire during a changeover in play on Monday.
Five-time Grand Slam winner Maria Sharapova suffered a shock defeat in the first round of the Qatar Open on Monday, dumped out in three sets by outsider Monica Niculescu.
Rafael Nadal is leading the latest ATP Rankings with 9,760 points while Caroline Wozniacki leads the Women's list with 7,965 points.
It was Serena Williams' first competitive match since winning her 23rd major at the 2017 Australian Open.
Roger Federer lies just 155 points behind the injured Nadal in the standings, with a possible 180 points available for making the last four in Rotterdam.
Venus Williams' win came in her 1,000th career match and her 22nd singles appearance in a tournament she first played in 1999.
Serena Williams had initially targeted last month's Australian Open but abandoned that goal after declaring she was not "where I personally want to be."
Ankita Raina continued her red-hot form with a fluent win after Karman Kaur Thandi's erratic victory as India blanked Hong Kong 3-0 in the Fed Cup here on Friday.
Sania Mirza has remained out of action since October 2017 with an injury in her right knee.