Carlsbad - Former world number one Martina Hingis is to make a competitive comeback playing doubles, six years after her second retirement.The Swiss star, who won five Grand Slam singles titles and nine in doubles, will play at the Southern California Open in Carlsbad from July 27 to August 4.She will partner Slovak Daniela Hantuchova, with whom she also played doubles in 2007 before her retirement."I am very much looking forward to making a return to competitive play at the Southern California Open," Hingis said."I remember winning the singles and doubles here in 1997 and winning the singles again in 1999."I feel in good shape at the moment after playing World Team Tennis. My competitive spirit is still very much alive and I love being out on court."Hingis retired for the second time in 2007 at the age of 27 having just discovered she had tested positive for a banned substance during her third round loss at Wimbledon that year.She tested for benzoylecgonine, a metabolite of cocaine, and opted to retire rather than contest the results.Although she maintained her innocence, she was banned for two years by the International Tennis Federation.She had first retired from tennis for two years at the tender age of just 22 in 2003, citing injuries as the reason.By this time she had already won all her Grand Slam singles and doubles titles and spent a total of 209 weeks as world number one.In 1996 she had become the youngest ever Grand Slam winner when teaming up with Helena Sukova to win the Wimbledon doubles title at just 15 years and nine months.She followed that up in 1997 by becoming the youngest ever Grand Slam singles winner at 16 years three months in the Australian Open before becoming the youngest world number one in history a couple of months later.Her second career, from 2005 to 2007, was nowhere near as successful as the first part as she never went beyond a Grand Slam quarter-finalHer second comeback comes hot on the heels of being inducted into the Tennis Hall of Fame.