The 24-year-old Harris served 16 aces in the third-round tie to beat the King of Clay 6-4, 1-6 and 6-4.

The win sees Harris advance to the quarter-finals where he will face the former US Open finalist, Kei Nishikori, of Japan.

Nishikori in his turn beat the South African-born Englishman, Cam Norrie, 3-6, 6-3 and 6-3.

Harris rates the win in the US capital city as the biggest to date in his career.

“Today was really special.

“I've had some big wins and I've beaten some Grand Slam champions, but to beat a 20-time Grand Slam champion in front of a full crowd with such an amazing atmosphere, it was definitely something very special.

“I would definitely put it up there as my best, for sure.

“I'm just super happy with how everything turned out.”

Harris and Nishikori have met once to date that resulted in a 6-1, 3-6 and 6-3 win for the South African earlier this year at the Dubai Duty Free Championships.

Harris and Nishikori battle it out at 1am on Saturday morning (SA time).

Lloyd OVERJOYED ???@lloydharris63 stuns Nadal 6-4 1-6 6-4 under the lights in Washington to reach the QF!#CitiOpen pic.twitter.com/qEmPHT8Psb

— Tennis TV (@TennisTV) August 6, 2021

@MorganPiek OFM Sport