Both teams can still qualify for the quarter-finals, but Mexico are in the stronger position of the two sides, currently sitting second in Group A.
David Notoane's side have left themselves with it all to do against Mexico, having not picked up a point yet in this summer's tournament after facing Japan and France.
Their opening game against the hosts was determined by Takefusa Kubo's 71st-minute strike, in a game which saw South Africa only register one shot on target.
South Africa improved in front of goal against France, scoring three in total with the goals coming from Kobamelo Kodisang, Evidence Makgopa and Teboho Mokoena, but it was not enough as Ronwen Williams conceded four at the other end of the pitch.
South Africa have only qualified for the Olympics on three occasions and in their previous two tournaments in 2000 and 2016 the nation were eliminated at the group stage, and they will need to score a few goals on Wednesday to prevent history repeating itself.
Mexico's Tokyo Olympics got off to a flying start when they put four past France last Thursday, and four different goalscorers found the back of the net including Ernesto Vega, Francisco Cordova, Carlos Antuna and Eduardo Aguirre.
Jaime Lozano's side were unable to repeat their opening day performance against Japan on Sunday, when they found themselves 2-0 down after 11 minutes, but Roberto Alvarado did add his name to the scoresheet five minutes from time.
Along with the defeat, more issues came from that game with Japan after centre-back Johan Vasquez was shown a straight red card in the 68th minute, and he will now be suspended for the final group game.
For Mexico to secure their place in the last eight, they can draw with South Africa and hope that France do not beat Japan, or to keep it in their own hands, three points on Wednesday will complete the job of progressing through.
Mexico have recent success in the Olympics having won the tournament in London 2012, but they only followed that up with a group stage elimination four years later in Rio.
South Africa opt for a 5-4-1 formation and the defensive line will need to improve on the four goals that they conceded against France to give their attacking teammates a chance of securing a victory.
The three goals that South Africa scored against France predominantly came from the left-sided players, with Kodisang scoring a goal and getting an assist, Singh also providing an assist and left-sided central midfielder Mokoena scoring South Africa's third.
Notoane's side need goals on Wednesday if they are to defy the odds and progress out of Group A, and therefore it is likely the manager will name the same side to the one that faced France due to the number of goals they managed to score.
Mexico centre-back Vasquez will be suspended for the final group game against Mexico - Vladimir Lorona is predominantly a right-back by trade but he can also play in the heart of the defence and is likely to replace Vasquez on Wednesday.
The Mexico starting lineup was unchanged for the opening two fixtures and apart from the forced swap at the back, Lozano is expected to remain with the same 11 again.
Goalkeeper Guillermo Ochoa is one of the three over-aged players in the Mexico squad, and the 36-year-old is also the most experienced at international level having earned 113 caps for the senior side.
South Africa Under-23s possible starting lineup:
Williams; Kodisang, Malepe, Fleurs, Mohamme, Frosler; Singh, Mokoena, Ngcobo, Cele; Makgopa
Mexico Under-23s possible starting lineup:
Ochoa; Aguirre, Lorona, Montes, Sanchez; Cordova, Romo, Rodriguez; Vega, Martin, Lainez
We say: South Africa Under-23s 0-2 Mexico Under-23s
Mexico will want to keep their destiny in their own hands and to do that they need three points on Wednesday, and after a struggling start to the Tokyo tournament for South Africa, Mexico should have the confidence to win at the Sapporo Dome.
With France chasing them for second spot, Mexico may feel some nerves on Wednesday but the experience of Ochoa behind the team could come in handy to push the side over the line and into the quarter-finals.