The American eagled the first, 10th and 11th holes at Sunningdale to finish at par 72 for a second-round score of 6-under 138, three strokes off the lead.
'I've never had two,' Diaz said. 'I know it's a record for me, and I was hoping it was an LPGA record.'
She tried for a fourth eagle at the 14th, but her 30-foot putt ran by the hole.
'I thought I hit a good putt, went past it, didn't even make birdie,' Diaz said.
Alice Ritzman had three eagles in the 1979 European Open at Sunningdale, along with Nina Reis at the 2006 Safeway Classic in Portland, Ore.
On the first hole, Diaz hit a driver off and played her second shot with a rescue club 214 yards to within 3 feet of the pin for a 3. At the 10th, her 4-iron second shot landed short of the green but bounced to within 30 feet and she made the putt.
At the par-4 11th, her 3-wood off the tee left her with a 56-yard wedge shot that rolled into the hole.