Onyango was named man of the match against Golden Arrows last night after pulling off a string of saves as Pitso Mosimane's side went top of the table for the first time this season after beating Abafana Bes'thende 2-0 at Princess Magogo Stadium.
Sundowns struggled in the first half but took control after the break as Hlompho Kekana scored the opener with a sweetly struck effort with the outside of his right foot in the 59th minute.
Modjeka Madisha added the second with a header in the 70th minute from a corner from evergreen midfielder Teko Modise.
And Onyango, who won the league in 2008/09 and 2009/10 with SuperSport United, and with Downs last season, is eager to repeat the feat but is wary of getting carried away with still six matches left.
"Definitely [I want to win a fourth league title]. There are a lot of guys as well who have won it many times and they want to win again," said Onyango, who won the Goalkeeper of the Season prize last term.
"Having said that, it is a challenge for us also to make history at the club. We believe that we can do it and the challenge rises ahead of us.
"But we are taking it easy and we are playing one game at a time. We know we are on top of the log at the moment, but it's not all over. We need to win our next three/four games to see where the league will go."
The Uganda captain was absent when Downs lost 1-0 to Arrows in the Nedbank Cup quarter-finals earlier this month, but was kept busy against Clinton Larsen's side on Friday. Onyango did particularly well to swiftly drop to his weaker left side to keep out a thunderous shot from Zimbabwean winger Kudakwashe Mahachi in the 57th minute.
"We knew that it was going to be difficult here against Arrows, they always give us problems. They've got energy, they've got the fight in them," said the 31-year-old keeper.
"I had to stay on top of my game because they played on the break and you cannot make mistakes. We knew they'll get chances, so I had to stay on top of my game.
"We also saw that the last time we played them in the cup they scored on the break. I had to do my best to keep the team in the game."
Onyango's big-match temperament will be needed again for Mosimane's outfit when they visit title rivals Bidvest Wits at Bidvest Stadium on Monday (17h00).