Brazilian forward Alan Kardec was awarded a special jersey to commemorate his 100th CSL appearance in Chongqing before the match.
"Hopefully we will renew our cooperation someday in the future. We are family as always," the club added.
Walter, who replaced Christian Alves in the 83rd minute, latched onto Jonathan Cicero's cross and needed just one touch before rifling a shot into the bottom right corner.
The "BVB" smoothed the way for their win with three first-half goals, while Dominic Volkmer's red card before half-time left Duisburg hopeless.
The Celta captain opened the scoring from Nolito's pass after 15 minutes in an entertaining match which saw Celta play some impressive football.
"Five, six, seven, eight! And jumping jacks," Cao Tingting, a 16-year-old girl shouted at the front of the class.
The 33-year-old Serb now faces a semifinal against Casper Ruud of Norway, who beat fourth seed Matteo Berrettini of Italy 4-6, 6-3, 7-6 (5).
The 22-year-old Osaka outlasted an inspired Victoria Azarenka from Belarus 1-6, 6-3, 6-3 in the US Open final on September 12 to clinch her second US Open title and third Grand Slam, following her victories in the 2018 US Open and 2019 Australian Open.
18-year-old Lorenzo Musetti of Italy, who had upset three-time Grand Slam winner Stanislas Wawrinka of Switzerland and Japan's top player Kei Nishikori in the tournament's opening two rounds, lost to Dominik Koepfer of Germany 6-4, 6-0.
The fact that the tie was decided with just one leg, rather than the traditional home and away format, meant the game was a potential banana skin for the Chinese-owned team making its first ever appearance in Europe, but Diego Martinez's side got off to a perfect start with two goals in 10 minutes.
Abdou Diallo was sent off for a second yellow cards after 65 minutes and Juan Bernat limped off the pitch in the 85th minute, which forced Tuchel's side to have to play with nine men for the last 10 minutes.