Tennis’s minor leagues are still a major challenge. The latest evidence arrived on Tuesday in Marbella, Spain, where Stan Wawrinka and Dominic Thiem, two of the game’s biggest achievers, launched a dual comeback at a low-level Challenger Tour event.

Neither had played in far too long, and neither won a set against players ranked outside the top 100, with Wawrinka losing, 6-2, 6-4, to Elias Ymer of Sweden, and Thiem following them to the main stadium and losing, 6-3, 6-4, to Pedro Cachin of Argentina.

“These guys, even on the challenger tour, their level is extremely high, and as you well know the difference between being 150 or being 50 in the world, there’s not a huge difference in tennis level,” said Daniel Vallverdu, Wawrinka’s coach. “Most of it is mental and luck.”

It was indeed a reality check for Wawrinka and Thiem, who once were ranked as high as No. 3 and are among the precious few to have made a splash in an era otherwise dominated by Rafael Nadal, Novak Djokovic and Roger Federer.

Thiem, 28, won the 2020 U.S. Open, becoming the first player outside the Big Three to win a Grand Slam singles title in four years. Wawrinka, who turned 37 on Monday, has won three Grand Slam singles titles, joining Andy Murray as the only man outside the Big Three to have won multiple major singles titles in the last 20 years.

But Thiem and Wawrinka are both far from their peaks, and Tuesday’s quick exits were a reminder of how far each has to go. Wawrinka had not played a match for nearly a year; Thiem for nearly nine months.

It showed.

“Rusty would be the word,” said Mark Petchey, the former ATP player who has coached Murray. “Challengers are a rough place.”

It is rare to see a star like Wawrinka or Thiem at this level, but hardly unprecedented. Andre Agassi dropped down and played two Challenger events at the end of the 1997 season when his ranking had fallen to No. 141. He used the experience as a building block to reconstruct his career, eventually returning to No. 1. His longevity was a model for this generation of enduring champions.

In his autobiography, “Open,” Agassi wrote that a tour official had likened his Challenger appearances to Bruce Springsteen playing a corner bar.

“What’s wrong with Springsteen playing a corner bar?” Agassi wrote.

Nothing at all, as long as the corner bar is packed with fans thrilled by their good fortune. Tuesday’s vibe in Marbella was far from electric, with the stands in the main Manolo Santana Stadium less than half full for both Wawrinka’s and Thiem’s matches. On average, only about 4,000 viewers were watching the livestream made available by the tour, but those numbers underplay the significance of Wawrinka and Thiem returning to action.

At different phases of their careers, with nine years between them, they are in similarly gray areas when it comes to their futures.

Wawrinka, suffering from long-term pain in his left foot, finally decided that he could take no more and underwent two surgeries, the first in March 2021 and then a second, more significant procedure in June that involved work on his Achilles' tendon. Thiem, who takes particularly aggressive cuts at his groundstrokes, injured his right wrist during a grass-court tournament on the Spanish island of Mallorca in June but did not resort to surgery, opting instead for immobilization with a splint and extensive rehabilitation.

He has repeatedly delayed his comeback, finally choosing to return on the red clay that remains his favorite surface. But one of Thiem’s strengths has been his ability to thrive in extended rallies, and on Tuesday his baseline game kept breaking down. He lost the first five games to the 228th-ranked Cachin before recovering and making it a match, but the frustration was audible down the stretch as he lectured himself, gesticulated between points and remained unable to break Cachin’s serve down the stretch.

Wawrinka was sluggish at the start as well, misfiring with his signature one-handed backhand. He briefly found his range early in the second set, going up two service breaks against the 131st-ranked Ymer. But Ymer, far quicker around the clay, reeled Wawrinka in by sweeping the last five games.

“Obviously looking at it from the outside it looks different, but for me and for Stan this match is a huge step in the right direction,” Vallverdu said by telephone. “The goal in the last six to eight weeks was to get back on court and to be able to do that without thinking about the body or any injuries. The fact he’s able to play a professional tennis match again is a huge step considering where he was about three months ago where from our perspective we didn’t even know if he would be able to play again.”

Wawrinka has said he did not want to end his career with an injury, similar to what Federer, his friend and Swiss compatriot, has said as he tries to work his way back at age 40 from his latest knee surgery and long layoff. For now, the only major winner in this golden era who has bid farewell, however informally, is Juan Martin del Potro. Even Andy Murray, with an artificial hip joint, plays on and has rehired Ivan Lendl as his coach to help him get the most out of his remaining years.

“I think for someone like Stan, the fact that the other guys are still around is definitely a factor,” Vallverdu said. “I think if one or two of them quit, it will have a bit of a domino effect.”

Wawrinka only resumed practicing on a court at the end of February, and, with the pandemic hiatus on tour in 2020, he has played few matches over the last three seasons. His next stop will be the Monte Carlo Masters, where he has a wild card and where the field, featuring most of the top 10, will be significantly stronger than in Marbella. Thiem plans to be there, too, after playing in next week’s tournament in Marrakesh, Morocco.

But evaluating their comebacks will take quite a bit longer. They need competition. They need the confidence that their bodies and shots will hold up on the points that matter most.