Before Roland Garros, Venus had never won a set in Paris in three previous appearances since debuting here in 2014.
Venus opted against heading to the stadium courts for practice on the eve of his quarter final.
"I had a long doubles match yesterday and then had mixed doubles so have taken it easier today" He said.
"I spent the morning reading a book and relaxing at the apartment and after lunch I hit a basket of balls with Ryan (off site) for an hour."
In the first round he and Harrison accounted for Argentine Diego Schwartzman and American Francis Tiafoe 36, 6-4, 6-4. They then played their best match of the tournament to date to beat Poland's Lukasz Kubot and Brazilian Marcelo Melo 6-4, 6-7, 6-3. They appeared down and out against then Indian pair of Purav Raja and Divij Sharan who served for the match at 6-5 in the second set. But Venus and Harrison broke back and went on to clinch a 4-6, 7-6 (7-5) 6-2 victory.
It improved on a record of six Grand Slam appearances where Venus had got to the third round, at Wimbledon in 2015 and 2016, the Australian Open in 2014 and 15, the US Open in 2014 and this week.
He will have some close support in the stands when he walks out on court.
"My girlfriend Sally has been able to travel with me for 5 to 6 weeks which has been a huge help for me off the court. My mum has made the trip over and so it has been great to be able to share this so far with both of them." Venus said.
Venus and Harrison are guaranteed to share 72,000 Euros (NZ$113,000) for making the quarter-finals. Win through to the semis and they will take away 132,000 Euros (NZ$208,000) between them.
Matt Brown is at the French Open thanks to Emirates Airline