HILVERSUM, Netherlands, Sept 6, 2012 (AFP) - A fine 63 enabled the tall Englishman to reach seven under, which put him two shots clear of Kaymer, who ended the day level with Fabrizio Zanotti of Paraguay and Frenchman Raphaël Jacquelin.
Kaymer's European team-mate Peter Hanson of Sweden was one of six players tied for fifth on four under, while Belgium's Nicolas Colsaerts - one of Jose Maria Olazabal's Ryder Cup picks - birdied the last to go round in 70.
But leading the way is Storm, who currently lies 114th in The Race to Dubai and faces a battle to retain his European Tour card.
In addition to struggling for form he has been forced to cope with tragedy away from the course, with his grandfather passing away prior to June's BMW International Open.
"I've had a tough run and it's all been a bit of a struggle. I've just not been enjoying it," Storm explained.
"I lost my grandfather on the Wednesday morning of Germany and since then I have really struggled. I kind of kept it to myself what happened but it hit me really hard.
"You can get punished round here but I played the best I have probably played all year. I'm just happy to get a round like that under my belt after recent months."
Focussing on the details of his opening round, Storm added: "I made the birdies when I gave myself the chances and got up and down when I missed the greens.
"The golf course here is fantastic - the best I have ever seen it - so you have to hit it straight and that is what I did.
"There is still a lot of play for this season. Keeping my card is the goal. At the start of the season it was getting into the top 60 on The Race to Dubai but I'm a long way from that so my goal now is to keep my card."
Kaymer and Jacquelin each benefited from eagles at the par five 12th en route to rounds of 65, although the former - champion here in 2010 - insists there is still hard work ahead as he seeks to recapture his best form.
"Two years ago when I won here was very nice but that was a period of time I could have played golf with my eyes closed," the German explained.
"Now is a different time when I need to work and it takes a lot of energy and a lot of concentration. I really need to focus on the things on the range. Two years ago it was more automatic."
Zanotti, who tied for second when Kaymer triumphed at this venue, managed to avoid any dropped shots, while Simon Dyson - three times a winner of this event and the defending champion - began the week with a 70 that featured an eagle on 18.
Leading first round scores in the European Tour KLM Open at Hilversum on Thursday (GBR and IRL unless stated, par 70):
63 - Graeme Storm
65 - Fabrizio Zanotti (PAR), Martin Kaymer (GER), Raphael Jacquelin (FRA)
66 - Peter Hanson (SWE), Craig Lee, Felipe Aguilar (CHI), Steve Webster, Alejandro Canizares (ESP), Danny Willett
67 - Andrew Johnston, Richard Bland, Shiv Kapur (IND), Paul Waring, Oliver Fisher, Paul Casey, Richard Kind (NED), Tommy Fleetwood, Gonzalo Fdez-Castano (ESP)
68 - Michael Campbell (NZL), Jaco Van Zyl (RSA), Reinier Saxton (NED), Bernd Wiesberger (AUT), Mark Foster, Henrik Stenson (SWE), Scott Jamieson
69 - Peter Lawrie, Steven O'Hara, Johan Edfors (SWE), Pablo Larrazabal (ESP), Joel Sjoholm (SWE), Marc Warren, Niclas Fasth (SWE), Benjamin Hebert (FRA), Marcus Fraser (AUS), Bradley Dredge, Chris Wood, Gareth Maybin, Phillip Price, Andrew Dodt (AUS), David Lynn, Shiv Shankar Prasad Chowrasia (IND), Lee Slattery, Andy Sullivan, Sam Walker, Miguel Angel Jimenez (ESP), Richard Green (AUS), Gregory Bourdy (FRA), Lorenzo Gagli (ITA)