World number one Iga Świątek has shown her class to guide Poland to the quarter-finals of the second annual United Cup mixed teams’ tennis tournament.

Swiatek hit the court under pressure on Monday, needing to win the women’s singles rubber against Spain’s Sara Sorribes Tormo to keep the tie alive at Perth Arena.

Alejandro Davidovich Fokina had given the Spanish a 1-0 lead with a spirited 3-6, 6-3, 6-4 comeback victory over world number nine Hubert Hurkacz.

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But Swiatek rose to the challenge with a crushing 6-2, 6-1 win over Sorribes Tormo to force a deciding mixed doubles rubber.

The four-time grand slam champion and Hurkacz then needed little more than half an hour to wrap up the tie 2-1 with a 6-0, 6-0 drubbing of Sorribes Tormo and Davidovich to make Poland the first nation through to the quarter-finals, as Group A winners.

Poland and Spain defeated Brazil in their other ties.

In Sydney, three-time grand slam finalist Casper Ruud kept Norway’s quarter-final chances flickering with victories in the singles and doubles against Team Croatia.

Donna Vekic had given Croatia an early 1-0 lead with a hard-earned 7-5, 3-6, 6-3 win over unheralded Malene Helgo.

But Ruud then clubbed Borna Coric 6-4, 6-1 to send the tie to a decisive mixed encounter, which Norway claimed in a match tiebreaker.

The 6-2, 3-6, 10-7 victory for Ruud and Ulrikke Eikeri over Vekic and Ivan Dodig leaves Norway (1-1) anxiously awaiting the outcome of the last remaining Group F fixture between Croatia (0-1) and the Netherlands (1-0).