The 20-year-old Greek, who has already won tournaments in Marseille and Estoril as well as reaching the final of the Masters 1000 in Madrid, is the youngest player in the top 20.
He has leapfrogged Alexander Zverev who dropped two places to seven.
It may be a brief visit to the top five for Tsitsipas with lots of points on offer at this week's Montreal Masters and Kei Nishikori, just five points behind him in sixth. Tsitsipas reached the final in Monreal last year while Nishikori bowed out in round one.
Novak Djokovic remains at number one, the 263rd week of his career that he has occupied the position. That is still 47 weeks short of record-holder Roger Federer (310) who stays third behind Rafael Nadal.
The biggest climber of the week is the Australian Nick Kygios who held his composure to beat Daniil Medvedev in Sunday's Washington Open final.
The Australian rises 25 places to 27, back to where he was at the start of last October and putting him within touching distance of a return to the top 20.
Medvedev moved up one place to nine with Fabio Fognini dropping out of the top 10.
ATP rankings as of August 5
...