AN Elliott Harris strike midway through the first half saw Hayle into the quarter-finals of the Supplementary Cup after a keenly fought local derby at The Saltings on Saturday.
"It was a classic game of two halves," said Hayle player manager Dean Mooney. "We had the better of the first half, but then had to defend really well as St Ives came back at us in the second half."
The only goal of the game came after 25 minutes when Marcus Smith, who had earlier hit the home bar with a free kick, put Harris through on goal for the visiting midfielder to round a defender before sliding the ball past advancing keeper Tony Simons.
Ashley Matthews went close to doubling Hayle's lead when he shaved the upright 10 minutes later as Hayle continued to have the better of the first half. But Chris Lock brought a fine save from visiting keeper Dave Allen just before half-time and from then on the home side began to dominate.
Hayle, however, were disrupted by a serious knee injury to full back Shaun Mitchell on 55 minutes which held the game up for 10 minutes before an ambulance arrived.
Ross Duncan saw a free kick cleared off the Hayle goal-line on 63 minutes and Lock, Martin Harding and Simon Carter all had shots blocked or saved by Allen.
But the visitors always looked dangerous on the break with Smith bringing a fine save from Simons and Sam Charlton and substitute Carl Shorthouse both shooting narrowly wide as they held on to claim victory thanks to stout defending by the back four, with Zac Williams, celebrating his 17th birthday, in outstanding form.
Even then they had to survive a strong shout for a penalty when Lock was brought down in the last minute, but home appeals were turned away by the referee.
St Ives: T Simons, B O'Hara, A Perkin, C Lock, M Allen (D Paynter 75), R Duncan, S Carter, J Hughes, R Cook, M Harding, M Fowler.
Hayle: D Allen, K Harris (C Shorthouse 35), Z Williams, D Mooney, S Mitchell (A Northall 55), G Stirr, A James, A Matthews, E Harris, M Smith, S Charlton.
Man of the match: Ashley Matthews (Hayle).