Australians John Millman, Alexei Popyrin and Alex de Minaur have all progressed at the Madrid Open after contrasting victories.
Millman saved three match points in his first-round clash before closing out his first win over a top-20 opponent in more than 12 months.
The 31-year-old exhibited his renowned toughness to battle back and overcome world No.16 Hubert Hurkacz 5-7 7-6 (9-7) 6-3.
Polish 12th seed Hurkacz, who last month claimed his maiden ATP Masters 1000 title in Miami, held match points during the second-set tiebreaker but could not put Millman away in a contest that lasted two hours and 22 minutes.
The victory was Millman's eighth career top-20 win - only his second on clay - and first since defeating Russian Karen Khachanov in Auckland in January last year.
His next opponent will be unseeded Briton Dan Evans.
Qualifier Popyrin accounted for last week's BMW Open runner-up Jan-Lennard Struff 6-3 7-6 (7-4) to set up a second-round meeting with Italian teenager Jannik Sinner, the 14th seed.
The 21-year-old Popyrin, who went into the tournament a career-high 76th in the rankings, will improve that irrespective of the result against Sinner.
De Minaur is through to a third-round meeting with world No.4 Dominic Thiem after scoring back-to-back wins for the first time since the Australian Open.
The passage for de Minaur was simpler than expected with South African Lloyd Harris retiring with a back injury while trailing 6-2 3-0.
In other second-round results, third-seeded Thiem dominated American Marcos Giron 6-1 6-3 in his first match in almost two months, sixth-seeded Andrey Rublev accounted for American Tommy Paul 6-7 (5-7) 6-3 6-4 while eighth-seeded Matteo Berrettini won a generational all-Italian battle 6-3 6-4 over Fabio Fognini.
Thiem hasn't won a tournament since breaking through with his first grand slam title at the US Open in September while Rublev, who has advanced to the quarter-finals or better in all seven tournaments he has played this season, is now 9-2 at the ATP Masters 1000 level in 2021.
Denis Shapovalov, the 11th seed, was knocked out by Alexander Bublik in the last 32.