World No.1 Simona Halep is the top seed at a Slam for the first time in her career. Can she fend off her five challengers in Melbourne? WTA Insider breaks down the No.1 scenarios ahead of the first Slam of the season.

MELBOURNE, AUSTRALIA - Five women have a chance to chase down World No.1 Simona Halep for the WTA's top spot at the Australian Open, which begins on Monday, January 15th. No.2 Caroline Wozniacki, No.3 Garbiñe Muguruza, No.4 Elina Svitolina, No.6 Karolina Pliskova, and No.7 Jelena Ostapenko all have a chance to leave Australia with the No.1 ranking.

Halep finished the 2017 season as the WTA's 13th year-end No.1, just edging Wimbledon champion Muguruza by 40 points. The top spot was in play during Week 1, with Halep, Muguruza, and Wozniacki all in action, with Halep increasing her point lead by winning the title at the Shenzhen Open and extending her No.1 run to 16 consecutive weeks.

Breaking down Halep's challengers for No.1:

Caroline Wozniacki

No.1 Scenario: Needs to reach the semifinals to have a chance.

After a resurgent 2017 season which saw her return to the Top 5 for the first time since 2015, Wozniacki will be a Top 2 seed at a Slam for the first time in six years. Her best result in Melbourne came in 2011 when she mad the semifinals. Since then she has advanced past the Round of 16 just once.

Wozniacki is bidding to return to the No.1 spot for the first time since January 2012. If she returns to No.1, it would be the longest gap between stints at No.1 since the computer rankings were introduced in November 1975. The current record belongs to Serena Williams (5 years, 29 days).

Garbiñe Muguruza

No.1 Scenario: Needs to reach the final to have a chance.

Muguruza became the youngest active player to hold two major titles with her stunning run to the Wimbledon title last year. The 24-year-old became the 24th WTA No.1 after the US Open and held that spot until a late-season surge pushed Halep ahead.

The Spaniard comes into Melbourne with some injury concerns, after picking up an upper leg injury in Brisbane. She achieved her best result in Melbourne last year, making the quarterfinals before losing to CoCo Vandeweghe.

Elina Svitolina

No.1 Scenario: Needs to reach the semifinals to have a chance.

The Ukrainian led the tour in titles last season and she picked up where she left off in Week 1, losing just one set en route to her 10th career title at the Brisbane International. The win earned her a Top 4 seeding in Melbourne, where she has yet to advance past the third round in five appearances.

Karolina Pliskova

No.1 Scenario: Needs to win the title, with other results falling in her favor.

Last season, Pliskova became the first player representing the Czech Republic to hold the No.1 ranking, doing so on the strength of her strong second half of 2016 and first half of 2017, in which she won two titles and made the semifinal at Roland Garros. Pliskova's best result in Melbourne came last year when she made the quarterfinals and lost to Mirjana Lucic-Baroni.

Jelena Ostapenko

No.1 Scenario: Needs to win the title, with other results falling in her favor.

The reigning French Open champion is still in search of her Slam-winning form this season. She has yet to win a set, losing in the opening round in Shenzhen to Kristyna Pliskova and in Sydney to Ekaterina Makarova. The 20-year-old will be making just her third main draw appearance at Melbourne Park this year.