The pair couldn't be separated after 36 holes and are both at 15 under par ahead of Sunday's final round
Willett And Rahm Share Wentworth Lead
The pair began at 11 under and each shot four under par 68s on Saturday, with both men mixing six birdies each with two bogeys.
They battled it out for much of the day but it will be the Englishman who will be feeling happier after closing a two-stroke deficit over the final two holes.
Watch: Drama at 18 ensures the pair are tied at -15
Rahm, looking for his fourth Rolex Series victory tomorrow, reached 16 under and went two clear of his playing partner after a birdie on 16.
It looked as if he was going to go three clear on the par-5 17th but he three-putted from around 12ft to fall to 15 under and just one clear of Willett.
He then pulled his drive left on the 18th and took an unplayable from the bushes before holing a 20 footer for par after finding the green from around 200 yards.
It was true grit shown from the Spaniard who looked to be coming off of the rails.
Willett, perhaps thinking he may take the lead, made an up-and-down from the back bunker to birdie after splitting the fairway with his drive to match Rahm.
The 2016 Masters champion looks in inspired form, whilst Rahm is also looking very near his best.
The weather does look to be an issue for the final round with rain and thunderstorms forecast in the late morning and early afternoon.
The pair have distanced themselves from the pack by three strokes and tomorrow looks to be an extremely exciting day if the weather holds off.
Shubhankar Sharma is in third at 12 under after a six under 66, but it could have been better for the Indian who needed an up-and-down from greenside on 18 to shoot 64 (-8).
That would have been the best round of the week, but the 23-year-old duffed his chip and then missed from short range for par.
He is tied with Justin Rose who also bogeyed the last from being greenside in two.
Rose eagled the 17th to reach 13 under, and four under for his round, but the dropped shot means he will have work to do to chase the leaders tomorrow.
Christiaan Bezuidenhout is also at 12 under after a 69 (-3).
The young South African had gone 39 holes without a bogey until his dropped shot at the 13th but he came back with a birdie on 17 to break 70 and put himself in contention for the final round.
The shot of the day belonged to Ross Fisher who holed a 4 iron from 225 yards on the 18th for an albatross 2.
The Englishman won a BMW i8 worth over £130,000 came home in 29 (-8) to reach 7 under par.
The round of day belonged to Rory McIlroy who shot a seven under par 65.
The World No.2 made the cut on the mark at +1 but reached six under after making six birdies and an eagle on Saturday morning.
BMW PGA Championship 3rd round leaderboard:
3 Shubhankar Sharma -12
3 Justin Rose -12
3 Christiaan Bezuidenhout -12
6 Richie Ramsay -10
6 Rafa Cabrera Bello -10
8 Patrick Reed -9
9 Andrew ‘Beef’ Johnston -8
9 Francesco Molinari -8
9 Andrew Putnam -8
9 Viktor Hovland -8
9 Paul Casey -8
9 Billy Horschel -8
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