ANTIPOLO — Harmie Constantino thrived on the par-5 No. 17 to salvage a two-over 74 and catch amateur hotshot Rianne Malixi at the helm, just a stroke ahead of Marvi Monsalve at the start of the ICTSI Valley Golf Challenge here Wednesday.

Constantino and Malixi took charge at the end of a punishing day where the lead routinely changed hands in furnace-like conditions at Valley South.

Constantino endured a pair of back-to-back bogeys with two birdies, the last on the penultimate hole that saved her a pair of 37s.

"I played okay but I could've have played better since there were a lot of putts that I could've made and a lot of up-and-downs that I could've saved," said Constantino who also flubbed a couple of birdie chances from close range.

Malixi, toughened up by a three-month stint in the US, held her ground against last year's Order of Merit champion in one of the featured flights and looked headed to wrest early control with a bogey-birdie card after four holes.

But she holed out with a double-bogey on the par-5 No. 5 then negated a birdie on the ninth with a missed green bogey on 15, dropping her to joint lead instead, also with a couple of 37s.

"Not good," said Malixi when asked to describe her round, ruing her day-long struggle with her irons.

"My iron game wasn't that good and it could've been better. I wasn't able to convert some putts, didn't make those that mattered," said the 15-year-old rising star.

Monsalve missed forcing a three-way tie in the early going of the P750,000 tournament with a flubbed par-putt on the challenging par-3 closing hole but her 75 put her on track for a crack at a breakthrough win in the tour put up by ICTSI.

Chihiro Ikeda, winner of the Eagle Ridge Aoki leg last July, also birdied the 17 but her 76 dropped her two strokes off the joint leaders in a tie with Sarah Ababa.

Ababa, who won at Sherwood in 2015, dropped three strokes on the tough par-4 13th and ended up with a pair of 38s.

Mafy Singson also caught up with the co-leaders with a birdie on No. 11 after making the turn at 38.

But the World Amateur veteran yielded three straight strokes from No. 12 and bogeyed two of the last three against a birdie on the 15th. She limped with a 77 for a share of sixth with fellow amateur Alethea Gaccion.