Dino Prizmic's run at the Plava Laguna Croatia Open in Umag came to a disappointing end, as the Croatian No. 1 fell short of reaching the quarter-finals. After coming within touching distance of a straight-sets victory over Slovakia's Alex Molcan in the second round, the momentum shifted dramatically. Trailing 0-4 in the deciding set, Prizmic was forced to retire, sending Molcan through with a 3-6, 7-6(5), 4-0 victory.

Prizmic made a sluggish start to the match, allowing the world No. 101 to strike first with an early break for a 2-1 lead. However, the Croatian responded impressively, reeling off four consecutive games to take firm control of the opening set.

In the second set, Prizmic looked to have one foot in the next round. He led 5-3 and, at 5-4, stepped up to serve for the match. But he was unable to close it out, as Molcan fought back to force a tie-break, which the Slovak claimed 7-5. Early in the decider, Prizmić had opportunity to break back immediately, earning a 0-40 lead at 0-1, but failed to convert. Shortly afterwards, hampered by physical issues, he retired from the match.

Prizmic's previous two ATP Tour quarter-final appearances had both come in Umag, where he was eliminated by the eventual champions on each occasion - Australia's Alexei Popyrin and Italy's Luciano Darderi.

"I ran out of energy during the second set. I started feeling weak already at 3-2," Prizmic said afterwards. "I tried to battle through and somehow finish the set, but in the third I simply couldn't continue. I've never experienced anything like this before. I still don't know exactly what happened, but I hope to recover as soon as possible."

The day also saw a number of major upsets, with top seed Flavio Cobolli of Italy and third seed Tomas Martin Etcheverry of Argentina both crashing out.

Cobolli, the world No. 9, was beaten 6-2, 6-4 by Argentina's Roman Burruchaga, who recorded by far the biggest victory of his career. Remarkably, all 13 of Burruchaga's ATP Tour wins have come on clay. He produced an outstanding performance, particularly in the opening set, where he did not face a single break point. Although he surrendered his serve immediately after taking a 4-3 lead in the second set, he responded with another decisive break that sealed the biggest win of his career.

"I'd played a really good match the day before, so I believed I could reproduce that level regardless of who was on the other side of the net," Burruchaga said.

Earlier this season, the Argentine came agonisingly close to winning his maiden ATP title in Houston, where he held three championship points before eventually losing the final to Tommy Paul. His father, Jorge Burruchaga, is a former Argentine football star best remembered for scoring the winning goal in Argentina's 3-2 victory over West Germany in the 1986 FIFA World Cup final.

Cobolli, who arrived in Umag as the world's ninth-ranked player, has now failed to progress beyond the second round of the tournament in all three of his appearances.

"Of course I'm disappointed," Cobolli admitted. "I feel at home here. I spent a lot of time near Umag when I was younger, in nearby Koper. After spending two weeks at Wimbledon, I didn't have as much time to readjust to clay as Román did, but he fully deserved the win."

Another seeded player to fall on Wednesday was Argentina's Tomas Martin Etcheverry, the tournament's third seed, who lost 7-5, 6-4 to 21-year-old Spaniard Daniel Merida, currently ranked No. 82 in the world.

The match appeared to be under Etcheverry's control when he opened up a 4-2 lead, but from that point on he won just one of the next eight games, allowing Mérida to seize the initiative and close out an impressive straight-sets victory.