PSG 0-1 Botafogo
Champions League winners Paris Saint-Germain were in shock following their narrow 1-0 defeat to Botofogo at the Rose Bowl on Thursday.
Igor Jesus scored the only goal of the game with a deflected shot after 36 minutes to leave the French side reeling.
The result saw the Brazilians move top of Group A with six points, after their opening day 2-1 victory over the Seattle Sounders.
PSG had kicked off their Club World Cup campaign with a comprehensive 4-0 win over Atletico Madrid, but despite creating numerous chances in this tie, the likes of Khvicha Kvaratskhelia and Goncalo Ramos were unble to find a way past Botafogo's resilient defence.
"A lot of people wondered, but we showed how strong Botafogo is," Jesus said after the game, on BBC.
Seattle Sounders 1-3 Atletico Madrid
Atletico Madrid bounced back from their 4-0 opening day defeat to PSG with a far more convincing showing against their American opponents.
Pablo Barrios opened the scoring at Lumen Field with his first goal on just 11 minutes. Axel Witsel was then on target two minutes after the break. Albert Rusnak pulled a goal back with 50 minutes played, but Barrios completed his brace just five minutes later to ensure all three points for his team.
Seattle take on PSG on Monday knowing they will be unable to qualify for the knockout rounds, but could still have an impact on proceedings. While Botafogo are in pole position with six points, both Atletico and PSG ended the evening with three points.
Inter Miami 2-1 Porto
Inter Miami came from a goal down against Porto in their second Club World Cup group clash to claim a 2-1 win.
Samu Aghehowa had opened the scoring for the Portuguese side from the penalty spot after just eight minutes but Inter were back on level terms when Telesco Segovia scored just after the half-time break.
And in typical Messi fashion, the Argentine attacker floated home a trademark free-kick, with 54 minutes on the clock, to secure the all-important win.
The result leaves Inter in second place in Group A with four points, level with leaders Palmeiras.
Palmeiras 2-0 Al Ahly
Brazilian Serie A side Palmeiras proved too strong for Egyptian giants Al Ahly in their second Group A clash at the MetLife Stadium on Thursday.
An own-goal from Wessam Abou Ali on 49 minutes got Palmeiras off the mark before Jose Manuel Lopez sealed the 2-0 win with his goal with 59 minutes on the clock.
Riveiro only took charge of the Egyptian side in May as a replacement for Marcel Koller.
He secured a goalless draw with Inter Miami in Al Ahly's first Club World Cup game, who now need a result against Porto on Tuesday if they are to have a chance of progressing to the knockout rounds.
The former Orlando Pirates boss said on iDiski Times: "The match was beyond our capacity. We tried to come back after the weather interrupted with a new style of play, but we failed to create enough opportunities."