Juan Martin del Potro said it would take time for him to build confidence after a four-month injury layoff, but it could be a speedy process for the Argentine after the tennis he displayed on Thursday night at the Delray Beach Open by VITACOST.com.

The top seed struck his forehand with authority and held his nerve in crucial moments to end the six-match winning streak of Reilly Opelka with a convincing 6-4, 6-4 victory. Del Potro didn’t face a break point and booked a quarter-final spot for the fourth time in five appearances in Delray Beach.

Del Potro has always been methodical about his comeback attempts, waiting until he’s fully ready to return rather than rushing back too soon. His performance on Thursday indicated that if his right knee continues to hold up, he can pick up where he left off at the end of last year.

A forehand error from Opelka at 1-1 in the opening set gifted del Potro an early break and the top seed held that momentum to take the early advantage. Little separated the two players in the second set, but a backhand error from Opelka on break point at 4-4 allowed the Argentine to serve out the match after 73 minutes.

Next up for del Potro is another American in Mackenzie McDonald, who required just a single break in each set to defeat Guillermo Garcia-Lopez 7-5, 6-4. This is the second ATP quarter-final for McDonald, who also accomplished the feat last June at the Ricoh Open.

Radu Albot of Moldova held off Nick Kyrgios of Australia to advance 6-2, 3-6, 6-3. The 29-year-old was especially tidy on serve in the deciding set, winning 80 per cent (20/25) of his service points to advance in one hour and 24 minutes. Albot is playing some of his best tennis, having reached his second ATP Tour semi-final earlier this month in Montpellier.

He’ll take on fourth seed Steve Johnson in the quarter-finals after the American held off Italian Paolo Lorenzi 7-5, 7-5. Johnson saved all six break points he faced and broke Lorenzi in the final game of each set to pick up the win after one hour and 57 minutes.

“I was having a hard time being accurate with my shots, so I’m glad I served well today,” said Johnson. “I’m happy I have a chance to play another competitive match tomorrow and hopefully clean things up.”

#NextGenATP Norwegian Casper Ruud continued to excel at the Rio Open presented by Claro on Thursday. Having reached his maiden ATP semi-final at this event in 2017, the 20-year-old defeated fifth seed Joao Sousa 6-3, 3-6, 6-4 to put himself into the quarter-finals again in Rio de Janeiro.

“I always play far away from home, but Rio always makes me feel very welcome,” said Ruud. “I feel the atmosphere here and it’s great to have the crowd on my side.”

Sousa dug deep after facing a break point to trail 1-5 in the final set, but Ruud hung tough to advance after two hours and 11 minutes. The Norwegian, currently No. 135 in the ATP Rankings, will make his Top 100 debut on Monday if he defeats Laslo Djere of Serbia on Friday.

“It’s a great chance for another 500-level semifinal,” said Ruud. “[Djere] is maybe the favorite in the [ATP] Rankings, but I’ve shown some good tennis before here and hopefully I can again.”

Ruud enjoyed success on the ATP Challenger Tour last year by finishing runner-up at $50,000 events in Braga and Francavilla. He also excelled on bigger stages by reaching the quarter-finals last July at the Swedish Open and coming through qualifying at the Australian Open, Roland Garros and US Open, advancing to the second round at the first two majors of the year.

Djere, who defeated top seed Dominic Thiem in the opening round, continued his inspired tennis with a 6-4, 6-2 victory over Taro Daniel of Japan. The World No. 90 didn’t face a break point against Daniel and won 83 per cent (20/24) of his first-serve points.

Pablo Cuevas of Uruguay produced a statement win over recent Cordoba Open winner Juan Ignacio Londero of Argentina 6-1, 6-4. The 2016 champion wasted no time getting down to business on Quadra Guga Kuerten, dropping just one point on serve (16/17) in the opening set. He continued to dominate the baseline rallies in the second set and secured the win after just 68 minutes.

Awaiting Cuevas in the quarter-finals is Albert Ramos-Vinolas of Spain, who scored an impressive 3-6, 7-5, 6-3 comeback victory over Federico Delbonis of Argentina. Delbonis served for the match at 5-4 in the second set, but Ramos-Vinolas rallied to advance after two hours and 20 minutes.

The Spaniard improves his FedEx ATP Head2Head against Delbonis to 2-3. Ramos-Vinolas trails his FedEx ATP Head2Head with Cuevas 1-6 and the Uruguayan has prevailed in their past five matches.

French wild card Ugo Humbert recorded the biggest win of his career on Thursday by beating World No. 12 Borna Coric 6-3, 6-3 in 80 minutes for a place in the Open 13 Provence quarter-finals.

“My level was good today, very positive,” said the 20-year-old Humbert, a contender to qualify at this year’s Next Gen ATP Finals in Milan. “The atmosphere was great, and it’s always easier when you aren’t the favourite. This was the first time I played a player ranked that high. I was able to stay calm and played well.”

View Marseille Singles Draw | Read More: Humbert Wins Fourth ATP Challenger Crown

Humbert, competing at a career-high No. 75 in the ATP Rankings, broke Coric’s serve three times and will next play German qualifier Matthias Bachinger, who was solid on serve in overcoming Fernando Verdasco, the fifth-seeded Spaniard, 6-4, 6-3 in 77 minutes.

“I watched Ugo in his last match,” said Coric, who will now travel to compete at next week’s Dubai Duty Free Tennis Championships. “I tried pretty much everything today. He returned well, mixed up his serve and didn’t miss many balls.”

Russia’s Andrey Rublev backed up his victory over three-time Marseille champion Jo-Wilfried Tsonga with a 6-3, 7-6(2) win over Matteo Berrettini of Italy in one hour and 37 minutes. He will next play Kazakhstani Mikhail Kukushkin, who beat fourth seed Denis Shapovalov on Wednesday.

Third seed David Goffin reached his first ATP Tour quarter-final of the season, battling past home favourite Benoit Paire 6-2, 6-3. After a pair of early breaks, the two were back on serve in the second until Goffin won the rally of the match and broke Paire for a 5-3 lead.

The usually quiet Belgian celebrated the break with a fist pump and a shout to the crowd. He will meet Gilles Simon for the fifth time in their FedEx ATP Head2Head series, which is tied at 2-2.

“Benoit can play very well. I’m happy with the victory tonight,” Goffin said. “I need to go through those kinds of matches in order to improve match after match. Every athlete goes through moments of doubt.”