The current Wimbledon and Australian Open title holders reached the Second Round after a straight sets (6-3, 6-4) win over Czech duo Petr Nouza and Patrik Rikl yesterday, before the Finn registered his second two-set victory of the day in the mixed doubles, alongside Kazakhstan's Anna Danilina.
But any thoughts of fatigue were quickly put to bed, as the number two seeds broke serve in the third game to take a 2-1 lead. They then broke again to take a 5-2 advantage, before wrapping up a 6-2 first set victory in just 27 minutes, having conceded just one point in their four service games.
Things did not get any easier at the start of the second set for Diallo and Fearnley, both ranked well outside the top 500 doubles players, as they only managed to save one of three break points.
However, they managed to force two break points in the next game, but failed to take advantage and Heliovaara and Patten took a 2-0 lead.
That set the tone for a second set in which the world numbers three and four were not quite as dominant on their own serve, but did more than enough to take a 5-3 lead.
With the chance to seal the win in front of them, the pair attacked their opponents serve, and after the first match point was saved, they sealed the straight sets win (6-2, 6-3) to reach the Third Round.
In the third round, they will face the winners of the match to be played later today - Frenchmen Sadio Doumbia and Fabien Reboul against India's Rohan Bopanna and Adam Pavlasek of the Czech Republic.
However, the next time the pair step onto court at Roland-Garros, it will be on opposite sides of the net! Heliovaara's mixed doubles win yesterday set up a Second Round match against Patten and Olivia Nicholls, to be played tomorrow.