Beatriz Haddad Maia suffered an embarrassing moment in her United Cup clash with Laura Siegemund on Sunday.

The Brazilian was desperate for a win in Perth after falling to an unlikely defeat against China's Gao Xinyu earlier in the week. But as she so often does, Haddad Maia found herself in the thick of a three-set battle as Siegemund refused to budge.

They were tied at one set apiece after German star Siegemund took the first 6-3 and Haddad Maia won the second 6-1. And the match was entering its vital moments when, at 3-3 in the decider, Haddad Maia wound up for a second serve to defend break point.

Incredibly, whether due to sun in her eyes or a sudden loss of belief, Haddad Maia tossed the ball and seemed to give up just before it hit her racket, sending it looping slowly over the net and way off target.

Siegemund immediately raised a hand of apology as the Australian crowd fell practically silent. Only when the umpire announced that the game was Siegemund's did a reluctant smattering of applause break out.

Haddad Maia would never recover from the break, as she put only one more game on the board in a 6-4 final-set defeat. After the match, Siegemund - ranked 63 places below Haddad Maia - said: "It’s the first match of the year against such a great player, it’s not easy.

"So I have to, out of the pocket, pull my best game basically, and I just tried to focus on that and stay cool in the [big] moments. The match, today, it wasn't perfect.

"For nobody it is, at the beginning of the year. But I tried to stay in it, I tried to stay positive, and hopefully that's giving me some confidence for the next matches."

Defeat to Siegemund meant the continuation of a frustrating few days for Haddad Maia, who was forced to serve underarm by painful cramps during her loss to Gao. Brazil have now lost both of their United Cup clashes, with China and Germany both getting the better of them.

Alexander Zverev made sure of Germany's win, with the world No. 2 dispatching Thiago Monteiro 6-4 6-4 in one hour and 17 minutes. "Last year we were playing a deciding match every single time so it's nice to know that we've got this one in the bag already," said Zverev.