Fluminense rallied in the second half to beat Ulsan 4-2 and knock out the South Korean side while Monterrey and River Plate ended goalless.

At Lumen Field in Seattle, Ryoma Watanabe got an early opening goal for Urawa Reds, who were backed by a noisy contingent of their supporters.

But captain Lautaro Martinez -- who got Inter's equaliser in their 1-1 draw with Monterrey of Mexico in their opening game -- repeated the trick to level matters with a clever overhead kick 12 minutes from time.

Valentin Carboni was then the unlikely hero as he grabbed the winner two minutes into injury time.

The 20-year-old Argentine had not played a competitive game since early October after suffering a serious knee injury while on loan at Marseille.

Carboni had not made an appearance for Inter in over two years, but he was on to hand to sidefoot home when the ball fell to him in the area.

"Our opponents play with their hearts and to counter that as a team we need to play with more pride, be humble and know how to suffer," Martinez told broadcaster DAZN.

The result left some Urawa fans in tears and Inter level on four points with River Plate with the two teams meeting next.

River Plate were let down by their finishing in a scrappy, foul-ridden encounter with Mexico's Monterrey, who sit on two points.

Esteban Andrada, Monterrey's Argentine keeper, made a series of saves while River's forwards were unable to put away the few chances that came their way.

Monterrey could still make it into the last 16 if they beat Urawa and River or Inter win their game.

- Bellingham strikes -

Earlier Jobe Bellingham got his first goal for Dortmund as his new club overcame stifling heat in Cincinnati to beat Sundowns 4-3 and move to four points from two matches in Group F.

The South African champions had taken a surprise early lead through a fine solo goal from Lucas Ribeiro.

However, Sundowns goalkeeper Ronwen Williams handed Dortmund their equaliser on a plate, passing the ball straight to Felix Nmecha, who stroked home.

Serhou Guirassy gave Dortmund the lead with his 35th goal since the beginning of the season.

English midfielder Bellingham, who this month followed older brother Jude's footsteps in joining the German side from Sunderland, started for the first time for Dortmund and made it 3-1 just before the break.

Khuliso Mudau's own goal made it 4-1 before the hour mark, but Sundowns salvaged some pride by reducing the deficit through Iqraam Rayners and Lebo Mothiba.

"I'm sweating like I've just come out of a sauna," said Dortmund coach Niko Kovac when asked about the conditions in a game which started at midday local time.

"It was tough going for both teams, but the opposition are used to it. We certainly didn't give our best performance, but that wasn't possible today."

Sundowns will still go into their final game in Group F with a chance of qualifying for the last 16.

"The boys made a wonderful performance... it was a hell of a match. I'm not happy but very proud," said their Portuguese coach, Miguel Cardoso.

South Korea's Ulsan gave Fluminense a real scare in their Group F clash at MetLife Stadium in New Jersey, leading 2-1 until the 66th minute before the Brazilians ran out 4-2 winners, eliminating the K-League champions in the process.

Colombian striker Jhon Arias put Fluminense ahead with a 27th minute free-kick but goals from Lee Jin-hyun and Um Won-sang gave Ulsan the advantage at the break.

Nonata levelled for the Brazilians in the 66th minute before Juan Freytes put Fluminense ahead in the 83rd minute, slotting home after a scramble in the box.

Keno added a fourth in stoppage time to leave Fluminense on top of the group, level on 4 points with Borussia Dortmund ahead of their final game against South Africa's Mamelodi Sundowns in Miami on Wednesday.

A win or draw for the Rio club in their final group game will ensure their passage into the last 16.