Fiorentina loanee Pedro put the hosts ahead with a low strike before Bruno Henrique converted from the penalty spot after a Leo Gomes handball.
The 12th seed poured out his intense emotions on the court, yelling at himself or his coaches after wasting several chances.
The Austrian, and two-time finalist in Roland Garros in 2018 and 2019, reached the fourth round in Paris for the five consecutive year.
The host squandered a promising chance after Axel Witsel failed to make the most out of Reyna's cutback pass into the penalty area.
"It's because I did a lot of things well. I played more aggressively than the previous days. I went to the net more often, and I hit a lot of winners," added the 12-time French Open champion, who needed only one hour and 35 minutes to see off his opponent.
With Sichuan's offense bogged down, Dongguan retook the lead and delivered the final blow with efficient offensive late in the fourth to make it 78-71.
Saturday ended with Newcastle United winning 3-1 at home to Burnley thanks to an excellent display from winger Allan Saint-Maximin. The Frenchman scored his side's first goal and then set up Callum Wilson for Newcastle's second of the game just four minutes after Ashley Westwood's 61st minute equalizer for the visitors.
Bayern Munich's transfer activities might serve as an example. The 2020 treble winner claims a loss of up to 100 million euros due to games behind closed doors and decreasing marketing profits.
The win, which came as the 35th from 36 matches this season, also ties him with Rafael Nadal for a record 14th Roland Garros quarterfinals appearance.
Also on Sunday Feyenoord was far too strong for Willem II in Tilburg. The home team went in front through Vangelis Pavlidis, but Ridgeciano Haps, Bryan Linssen and a brace by captain Steven Berghuis earned Feyenoord a convincing 4-1 win. AZ drew 4-4 at Sparta after surrendering a 4-0 lead in Rotterdam.
The signings of Callum Hudson-Odoi (Chelsea) Sergino Dest (Ajax) failed due to the Blues demand to implement a buying-obligation and Barcelona surpassing Bayern's 20 million offer.