The upset ended a sensational 17-month 56-match unbeaten Tour run by Nicol David – but the 25-year-old from Penang, who had not previously tasted defeat since the World Open in Madrid in October 2007, extends her undisturbed reign as world number one to 33 months.
But Grainger is enjoying a rejuvenation of her illustrious squash career. The KL Open triumph marked the 31-year-old's third successive WISPA World Tour title of the year, and the 22nd of her career – and she achieved it in her 40th final.
The WISPA President returned to her homeland to pick up her third US National title in a row, then moved into lobbying mode by joining fellow Olympic Ambassadors to promote her sport's bid for inclusion in the 2016 Games at the Sportaccord meeting in Denver.
Natalie Grinham, the former world No2 from the Netherlands, slips to four in the list – below her Australian sister Rachael Grinham for the first time since last September.
While the English trio of Jenny Duncalf, Alison Waters and Laura Lengthorn-Massaro retain fifth, sixth and seventh places, respectively, their England team-mate Tania Bailey – still recovering from knee surgery last year - jumps three places to 15 after a long-awaited Tour win at the NSC Series No5 in March in Kuala Lumpur.
1 [1] Nicol David MAS
2 [4] Natalie Grainger USA
3 [3] Rachael Grinham AUS
4 [2] Natalie Grinham NED
5 [5] Jenny Duncalf ENG
6 [6] Alison Waters ENG
7 [7] Laura Lengthorn-Massaro ENG
8 [8] Omneya Abdel Kawy EGY
9 [9] Madeline Perry IRL
10 [10] Isabelle Stoehr FRA
11 [12] Shelley Kitchen NZL
12 [11] Vanessa Atkinson NED
13 [13] Kasey Brown AUS
14 [14] Rebecca Chiu HKG
15 [18] Tania Bailey ENG
16 [15] Samantha Teran MEX
17 [17] Annie Au HKG
18 [16] Jaclyn Hawkes NZL
19 [20] Lauren Briggs ENG
20 [19] Raneem El Weleily EGY
Issued by Howard Harding on behalf of WISPA