South African Branden Grace (68), Marc Warren (67) of Scotland and Austrian Bernd Wiesberger (68) were also on 203.
"I have a good feeling for tomorrow and I want to try to get my first win," Grillo told reporters. "This is what I play for, this is what I have practised for my entire life.
"I have a great chance of taking my first trophy home. You have to learn first how to win out here and I think I’ve learned a lot, I think I'm ready."
Warren, Grace and Wiesberger have combined for 10 previous tour wins and will fancy their chances of capturing the first prize in Qatar.
"The last few years I've shown a lot of progress and come close a couple of times," said Warren.
"I didn't quite get it over the line and that was something that came quite easy at the start of my career as every time I was in contention I seemed to win."
World number two Henrik Stenson's hopes of landing a record fifth win in the Middle East are over after he carded a 71 for 212.
Fifth-ranked Justin Rose (69) was also down the field on 210 while defending champion Sergio Garcia slumped to a 77 for 215.
(Editing by Mark Meadows)
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