Melbourne, Australia (SportsNetwork.com) - World No. 1 and last season's rookie sensation Lydia Ko fired a 3-under 70 in Friday's second round and she is tied for the lead with a pair from this year's rookie class, Ha Na Jang and Ariya Jutanugarn, heading into the weekend at the ISPS Handa Women's Australian Open.

Ko, who turned pro at the beginning of the 2014 campaign and picked up three victories along the way, finished 36 holes at 6-under-par 140. Jang carded a 4-under 69 and Jutanugarn shot a 2-under 71, joining Ko in the lead.

A five-time winner on the LPGA Tour, including two as an amateur, the 17-year- old Ko won last year's season-long Race to the CME Globe and also became the youngest world No. 1 ever almost three weeks ago. Jang and Jutanugarn have never won on tour.

Charley Hull (71) finished her second round on the Composite Course at Royal Melbourne Golf Club at 4-under 142 and she is alone in fourth, while Amy Yang (70) and Jessica Korda (71) are tied for fifth at minus-3. Gwladys Nocera (72) is one shot further back at 2-under 144.

Defending champion and Australian Karrie Webb struggled on her way to a 5-over 78, but she narrowly hung on to make the cut at 5-over 151. First-round leader Ilhee Lee carded a 9-over 82, dropping her all the way into a tie for 51st at 4-over 150.

Ko, playing the back nine first to start her round, did all of her work on her opening eight holes. The teenager from New Zealand got into red numbers early with a birdie on her first hole at No. 10, but she gave that shot right back with a bogey on No. 11.

Following a par on 12, Ko knocked in her second birdie on No. 13. On the par-4 15th, Ko holed out for eagle from the fairway with a 9-iron, vaulting her up to minus-6.

"I made eagle on 14 yesterday and then I was angry that I came off with a par today. I felt like it was a hole that I could easily come off with a birdie. I was kind of angry and that kind of anger led me to hit an aggressive drive on the 15th," said Ko. "I was on the left edge of the fairway and I had 136 or something like that and I said 'eight could be a little long,' so I decided to punch a nine iron, and it landed just left of the pin and the mouth kind of feeded it right to the hole."

While she gave one of those shots back with a bogey on 16, Ko drained another birdie on the par-5 17th. That was it for Ko, however, as she coasted to the finish with 10 straight pars from No. 18, ending with her second straight 70

Jang, also playing the back nine first, started off on fire with three birdies over her first five holes at 10, 11 and 14. Jang tripped to her first bogey on No. 16 and then made the turn with three straight pars from 17.

Back-to-back birdies on two and three got Jang back on track, but another bogey on four dropped her back to minus-5 for the week. Following a trio of pars from five, Jang joined the leaders at 6-under with a gain on No. 8 and she finished up with a par at No. 9.

"I think it was better today. I think it's more simple thinking, only fairway and then green and two putt," Jang said. "So no pressure, I'm feeling better today."

Jutanugarn, who entered the day alone in second behind Lee, had a rough start over her first eight holes as she managed to make six pars and two bogeys on one and six.

The final 10 holes served Jutanugarn much better, however. A birdie on No. 9 seemed to fuel the rookie as she went on to make eagle on the par-5 10th. Over her final eight holes, Jutanugarn made seven pars and a birdie on 14 to grab a share of the second-round lead.

"Today's pretty good, but yesterday I made more putts," Jutanugarn admitted. "I missed some short putts today ... I had a three-putt on the first hole that wasn't a great start, but I made a couple later on."

NOTES: The only other time Ko held a share of the second-round lead, she went on to win for the first time on the LPGA Tour as an amateur, cruising to a 5- shot win at the 2012 CN Canadian Women's Open ... Jang's 4-under was the low round of the day ... The average age of the top-4 players on the leaderboard is 19 years old, with Ko being the youngest at 17 ... Jang finished tied for second at the season-opening Coates Golf Championship, while Jutanugarn did the same at the Pure Silk-Bahamas LPGA Classic two weeks ago ... With the cut falling at 5-over 151, 73 players advanced to play the weekend.