KATIE BOULTER came close to claiming the biggest scalp of her career today as Iga Swiatek edged a three-set thriller to knock Great Britain out of the United Cup.

Swiatek, the world number two, prevailed 6-7 (4) 6-1 6-4 in an epic contest just short of three hours to steer Poland into the semi-finals in Sydney.

The turning point came in the third set with Boulter leading 2-1 and a break up, with Swiatek heading to the physio room for a medical time-out and appearing to be in some discomfort.

The five-time grand slam champion was able to gather her composure, however, and broke Boulter’s serve to love on her return.

Although Boulter had a break point at 4-4 when she was denied by a brilliant backhand that just caught the line, Swiatek finally got the better of the world number 24 in their first meeting.

“The match was crazy, like so many changes of momentum,” Swiatek said in her on-court interview.

“I thought I had it under control in the first set, but I got tight and I didn’t want to make the same mistakes in the third.

“It’s hard to be precise under so much pressure, but I made it and it’s a step forward.”

Despite an instant Swiatek break at the Ken Rosewall Arena, Boulter showed her resilience during a third game of nine deuces on the Pole’s serve.

Boulter was unable to accept any of the four break points which came her way, but was in no mood to give up the opportunity when it next arose.

The British number one broke back to make it 4-3 and then held her next serve to love before taking it to a tie-break she dominated.

Swiatek responded in devastating fashion as Boulter struggled to cope with her accurate ground shots in the second set.

Boulter was brilliant in the final set but Swiatek held her nerve during countless stunning rallies to give Poland a match-winning 2-0 lead before the mixed doubles finale.

Hubert Hurkacz earlier overcame Billy Harris 7-6 (3) 7-5 in one hour and 45 minutes in the men’s singles match.

Harris made a manful attempt to bridge 109 places on the world rankings, forcing a tie-break after saving two set points.

The Nottingham right-hander raised British hopes by having three break points for a 2-0 lead in the second set.

But Hurkacz’s power and big serve provided decisive with 18 aces getting him over the winning line.

Olivia Nicholls and Charles Nicholls lost the dead mixed doubles rubber as Polish pair Maja Chwalinska and Jan Zielinski won 6-2 7-6 (3) to complete a 3-0 whitewash at 12.45am local time.