PERTH  - Andrea Petkovic's 2013 campaign has suffered a potentially catastrophic setback before the New Year has even begun, with the German struck down by a knee injury at the mixed teams Hopman Cup on Saturday.

The injury-plagued Petkovic appeared hampered by a right knee problem late in the opening stanza of her singles match against Australian teenager Ashleigh Barty, but still managed to win the first set 6-4. The former top 10 player sought treatment at the end of the first set and broke down in tears while being attended by the trainer. With her right knee heavily strapped she returned to the court, but the 25-year-old did not even manage to play another point, instead retiring from the match in tears, throwing her upcoming Australian Open campaign into serious doubt.

Petkovic had been ranked as high as ninth in the world in 2011, but slipped outside the top 100 this year due to injuries, with back and ankle problems seeing her end the year at 126 in the rankings after playing just 23 matches for the season. She had surgery on a torn anterior cruciate ligament in her right knee in 2008 and last year tore the meniscus in the same knee. Her retirement handed Australia a 3-0 win in the Group A tie, with the Germans forfeiting the mixed doubles and Bernard Tomic earlier beating Tommy Haas in three sets. In the men's singles, veteran Haas did everything but beat the 20-year-old Tomic, the Australian eventually prevailing 7-6 (8/6), 3-6, 7-5 in a match the German generally controlled.

The German, ranked 21st at age 34, had a seemingly insurmountable 6-1 lead in the first set tie break, but then inexplicably lost the next seven points to hand the Australian the set. Haas levelled the match and appeared to be cruising through the deciding set after an early break, until he served for the match at 5-4. Tomic, ranked 52nd, broke back to level the set, held serve and then broke Haas again to take the match.

"I don't know how I got out of that tiebreak," Tomic said after the win. Earlier on the opening day, the Spanish pairing of Anabel Medina Garrigues and Fernando Verdasco notched a 2-1 win over South Africa in sweltering heat. The singles rubbers were split in the Group B tie, with Medina Garrigues beating Chanelle Scheepers and Kevin Anderson upsetting Verdasco before the Spaniards proved too strong in the deciding mixed doubles.

The fourth seeds for the eight-nation tournament, Verdasco and Medina Garrigues, won the doubles in a match tiebreak, 6-4, 6-7 (3/7), 10-8 on a day where the mercury reached 40C (104F). Anderson notched his first win over Verdasco in three attempts in the opening men's singles match, despite being ranked 13 places below the Spaniard at 37. The South African had chances to break the remodelled Verdasco serve in the first set, but made amends in the tiebreak and then went on to win in straight sets, 7-6 (7/5), 6-4, in one hour and 43 minutes. Medina Garrigues, ranked 50th, had too many shots for the 60th-ranked Scheepers, the two players trading blows from the back of the court in some lengthy rallies. Scheepers had won their only previous encounter and held 11 break points to the Spaniard's eight during the match, but Medina Garrigues came from a break down in the first set to win 6-4, 6-2.