MELBOURNE, Australia — Fifth-seeded Ana Ivanovic struggled with her serve and lost in three sets to Czech qualifier Lucie Hradecka in the first big upset of the Australian Open on Monday, Ivanovic’s worst result in a major since 2011.

The former No. 1-ranked Ivanovic, a finalist at the 2008 Australian Open, breezed through the first set in 21 minutes with three service breaks before No. 142-ranked Hradecka started to find her range.

Ivanovic, who had a tour-leading 58 match wins in 2014, had 10 double-faults and made 30 unforced errors.

Hradecka clinched it on her first match point, making amends for her first-round loss to Ivanovic at Wimbledon in 2009 when she wasted a match point.

Third-seeded Simona Halep continued her strong start to the year with a 6-3, 6-2 first-round win over Karin Knapp of Italy.

Halep, who opened the season by winning the Shenzen Open in China, was a quarterfinalist at last year’s Australian Open, losing to eventual finalist Dominika Cibulkova.

After an early exchange of service breaks, Halep clinched the first set by breaking Knapp’s serve.

She clinched the match by also breaking Knapp’s serve.

The 23-year-old Romanian moved steadily up in the rankings last year, rising as high as No. 2, after winning two titles and making it to the final of the French Open, where she lost to Maria Sharapova.

Two-time Grand Slam champion Andy Murray beat Indian qualifier Yuki Bhambri 6-3, 6-4, 7-6 (3) to begin another quest to win an elusive Australian Open title.

Playing in the newly refurbished Margaret Court Arena, Murray trailed 4-1 in the third set before coming back to level the set and then dominate Bhambri, the 2009 Australian Open junior champion, in the tiebreaker.

Murray has reached the final of the Australian Open three times, losing to Roger Federer in 2010 and Novak Djokovic in 2011 and 2013.

In between his losses to Djokovic, Murray won his first major at the 2012 U.S. Open and followed that up with a second Grand Slam singles title at Wimbledon in 2013.

Tenth-seeded Grigor Dimitrov defeated Germany’s Dustin Brown 6-2, 6-3, 6 -2 in a 69-minute first-round match.

Playing on the second show court at Melbourne Park on a sunny but cool opening day, Dimitrov had little difficulty advancing to the second round and a match against either Lukas Lacko of Slovakia or Maximo Gonzalez of Argentina.

Dimitrov, nicknamed “Baby Fed” because of the similarity of his game to Roger Federer’s, won titles on three surfaces last year and reached his first major semifinal at Wimbledon, where he beat 2013 champion Murray in the quarterfinals before losing to eventual champion Novak Djokovic.