The victory puts the two-time champions within sight of the last eight, keeping them on course to add to the title won in 2013 and 2015.
The Brazilian international struck with 15 minutes remaining of a hard-fought game at the Tianhe Stadium to give the Guangzhou the advantage ahead of next week's second leg in Japan.
The first half started in a cagey fashion but Guangzhou, coached by 2002 World Cup winner Luiz Felipe Scolari, had the best of the exchanges in the first half and came close after 15 minutes.
After good approach play from Paulinho, Alan found himself one-on-one with Kwon Sun-tae in the Antlers goal only for the Korean shot stopper to make the save.
Soon after, the Japanese team, who were finalists in the 2016 FIFA Club World Cup, should have taken the lead. But central defender Kento Misao, only in the team due to absences, headed over from a good position.
Guangzhou dominated much of the second-half. Eight minutes in, Ricardo Goulart missed perhaps the best chance of the evening to date, heading over from close range.
Despite the fact that this was the first leg, the game started to open up. Midway through the second half, substitute Yu Hanchao forced another save from Kwon.
Guangzhou continued to push forward and were rewarded 15 minutes from time.
Kashima failed to clear a corner from the right and Paulinho was there at the far post to fire home from close range.
"We worked hard to get the first goal and we kept going until it came" said Scolari. "But there is still the second leg remaining and we know that it will be tough against Kashima next week. We will have to be at our best."
Thailand champions Muang Thong United, playing a first ever knockout match in the tournament, let a first-half lead slip at home to Japan's Kawasaki Frontale to lose 3-1.
Deep into first half injury time, Teerasil Dangda sent the Thai fans wild with delight. There seemed to be little danger when he collected the ball outside the area, but a clever dummy from Theerathon Bunmathan gave the striker a little space, and he turned to fire home.
A defensive error after 65 minutes allowed Kawasaki to equalise. Muang Thong's Japanese centre-back Naoki Aoyama misjudged the flight of a ball floated into the area to leave Kengo Nakamura unmarked around the penalty spot, and the former Japanese international fired past Kawin Thamsatchanan into the net.
Within three minutes, the J.League team took the lead in exquisite fashion. Akihiro Ienaga crossed from the right for Yu Kobayashi to volley high into the Thai net.
Muang Thong pushed forward, but were unable to get a goal and were caught in the final moments.
Kobayashi squared the ball from the right and there was Hiroyuki Abe to side-foot home at the far post.
It leaves the Thai champions with a mountain to climb in Japan next Tuesday if they are to match Buriram United's last eight appearance in 2013.
