Ecuador were forced to play with 10 men from the 22nd minute of the game at Levi Stadium when striker Enner Valencia was sent off for dangerous play.
The 34-year-old forward struck the chest of Venezuela defender Jose Martinez with his boot while challenging for a high, bouncing ball in the box and was initially awarded a yellow card but after a VAR review he was shown a straight red.
Ecuador, which had been in control of the game before the dismissal, responded well and went ahead in the 40th minute when Venezuela failed to clear a free-kick into the box and Jeremy Sarmiento pounced on the loose ball to drill home.
Venezuela head coach Fernando Batista made two changes at the break, bringing on Cadiz and Bello and both were to make a decisive impact.
"Vinotinto" striker Salomon Rondon laid the ball off to Cadiz, whose low side-footed shot from the edge of the box took a slight deflection as it flashed past Ecuador keeper Alexander Dominguez.
Then, in the 74th minute, Alexander Gonzalez whipped in a cross from the right, met with a diving header from Rondon which was parried by Dominguez but Bello reacted to fire home the loose ball.
"To be able to score a goal, which helped in the victory, and to have contributed to the first goal, is a joy. These three points are very important for what's to come," said a delighted Bello.
Ecuador's Spanish coach Felix Sanchez said the red card for Valencia had forced him to change the team's approach.
"We had to change the plan, wait a bit behind the opposition. It's clear that when you play with 10 men you are at the mercy of the opposition for many minutes, even if you don't want to play that way," he said.
"Obviously it's not the dream start, but there are two more games left and we have the team to compete. The most important thing is that the team recovers its spirit for what is to come."
Later on Saturday in Group B, Mexico face Jamaica.
