With the four top seeds absent until the main draw, Romania’s Ovidiu Ionescu - ranked six - is the second highest seed involved in the men’s singles at this stage, but he lost 11-7, 12-10, 10-12, 11-9, 11-5 to Spain’s Jesus Carteno, ranked 18 places below him.

There was also defeat for his 2019 World Championships men’s doubles companion, seventh-seeded Spaniard Alvaro Robles.

The latter lost a three-game lead in the Pavilhão Multiusos de Guimarães as Belarus number 21 seed Aliaksandr Khanin fought back to win 3-11, 9-11, 6-11, 11-8, 11-7, 11-6, 11-9.

Britain’s Paul Drinkhall, seeded fifth, managed to live up to his ranking as he beat Turkey’s Ibrahim Gunduz 11-9, 11-4, 11-4, 11-7.

In the women’s group matches, Drinkhall’s compatriot Charlotte Carey began with a flourish.

Carey, seeded 25^th, came from two games down to defeat the highest seeded group stage player, Debora Vivarelli of Italy, 8-11, 9-11, 11-8, 12-10, 11-9.

Five men and four women will earn places at the Olympics via this competition.

There are 36 men and 40 women on the entry list for the competition and the top four seeds have been granted entry to the main draw, with all remaining players required to compete in an initial phase comprising 10 groups of three or four players.

But Carey will be proceeding with confidence after such a victory.

Seeded two positions below Carey, Turkey’s Sibel Altinkaya also showed the right stuff in winning an arduous match against the higher-ranked Luxembourg player Sarah De Nutte 12-10, 10-12, 7-11, 12-10, 11-8, 11-9.

Ukraine’s 28^th seed Solomiya Brateyko also provided an upset as she beat Spanish number eight seed Galia Dvorak 14-12, 11-7, 11-4, 9-11, 9-11, 11-7.

And the Belarusian number 13 seed, Daria Trigolos, also suffered a shock defeat at the hands of Lithuania’s Kornelija Riliskyte, seeded number 36, by a score of 11-2, 6-11, 5-11, 16-14, 11-5, 11-6.

Denmark’s 34-year-old Mie Skov, seeded 39^th after coming out of retirement to try and reach the Olympics, recovered from a two-game deficit to force Croatia’s Mateja Jeger down to the wire, but the number 18 seed held her nerve to win 11-6, 11-6, 8-11, 8-11, 13-11, 10-12, 11-8.

The route to Olympic places is not straightforward, particularly for players at this stage.

Those in first and second positions in the groups will advance to join the top four seeds in a draw of 24 players.

Eight will receive first round byes, while players from the same National Olympic Committee will be on opposite sides of the bracket, as will the two qualifiers from each group.

The two finalists will confirm their spots at the Games, but the final will not be played.

After that, the other 22 players who did not make the final will compete in a second tournament for three men's and two women's spots.

The losing semi-finalists in the second men's tournament will play for the final spot, joining the two finalists at the Games.