Pirates lost 4-1 to Downs in a league match last weekend at Loftus Versfeld Stadium, failing to close the gap between them and the Brazilians.
The loss now sees the Bucs trailing Downs by nine points, with the Brazilians having collected 42 points in 15 games, while Pirates have managed to secure only 33 points.
Despite the defeat, Riveiro believes his squad is still strong and that they could have easily won the match had they taken their goal-scoring chances. However, he acknowledges that Sundowns were the better side on the day.
"The difference between the two teams will show at the end of the season, after 30 games," said Riveiro.
"Then we will see if we are on the same level, or if the difference is big, or if it's not. But today [Saturday] is just one game.
"The game can go in different directions. If we had scored in the first half, although in my opinion, Sundowns were better than us."
Mandla Ncikazi has credited Orlando Pirates for playing a significant role in his development as a coach, insisting that maintaining good relationships helped pave the way for his return to Golden Arrows.
Orlando Pirates head coach Abdeslam Ouaddou has challenged his players to believe they can end the club's 31-year wait for a second CAF Champions League title after securing their place in the group stages.
Mamelodi Sundowns coach Miguel Cardoso has admitted that his team's mistakes and failure to manage their emotions proved costly as they suffered a shock elimination from the CAF Champions League.
Orlando Pirates breezed into the CAF Champions League group stage after a dominant 4-0 victory over Namibian side African Stars at the Orlando Stadium to secure a 5-0 aggregate victory.
