Gimenez rose perfectly to meet a Carlos Sanchez free-kick and score the goal that broke a 48-year Uruguayan 'curse' of failing to win in the opening game of the World Cup finals.
Egypt came within minutes of surviving largely thanks to the heroics of goal-keeper Mohamed El-Shenawy, who bravely dived to snatch the ball from Luis Suarez' feet and then flung himself through the air to tip a Edinson Cavani volley wide.
Uruguay gained in strength and purpose as the game progressed and it became clear that Salah, who injured his shoulder last month, was going to stay on the bench.
Before that, Egypt had rarely looked in trouble in a scrappy match at the less-than-packed Yekaterinburg Arena, though without Salah they also did little to threaten the Uruguay goal.
Suarez squandered a great first half chance by firing into the side netting when the ball broke loose after a corner, and forced another good save from El-Shenawy in the opening moments of the second period.
Salah's absence came as a surprise after Coach Hector Cuper had said on Thursday he was almost 100 percent certain to play.
The Liverpool striker, who turned 26 on Friday, injured his shoulder in the Champions League final against Real Madrid, and millions of Egyptians had been on tenterhooks to see if he would recover in time for the tournament.
He now has four more days to work on his fitness before Egypt face Russia in St. Petersburg next Tuesday, while Uruguay will play Saudi Arabia the next day in Rostov.
Uruguay's Jose Gimenez scores their first goal