Jennings had a humdinger battle with Mount Maunganui's Matthew Champness on his way to a 17th-hole victory.
It was a par-fest on the back nine, with both players refusing to give an inch but a couple of missed putts on the 16th and 17th sealed Champness' fate.
Jennings was happy enough with his performance but said he would need to lift his game against quarterfinal opponent Ron Sisson (Omanu), who was only a couple over the card in his win.
Among the others to advance in the senior division was top qualifier Peter Rankin of Royal Wellington.
Gisborne players are scattered throughout the 80-strong men's field split into five divisions.
Tene Goldsmith (Poverty Bay), the top seed in the senior reserve division, moved into the quarterfinals with a 3 and 2 win.
He was joined there by his Bay clubmates Carl Carmody, Richard Foon and Clive Dean.
Goldsmith's younger brother Kitt is still in the running in the intermediate division, alongside Gisborne district councillor Larry Foster.
The intermediate reserve division features a handful of locals who negotiated the first matchplay round — Bill Simpson, Warwick Thompson, Alan Baldwin, Brian Hall and Keith Daniels, all of Poverty Bay, and Electrinet Park's Barry Cox.
The junior division quarterfinalists include Poverty Bay's Brian Read.
Marg Colebourne continued her impressive form in the 20-strong women's competition.
Colbourne added 87 to her opening round of 85 to be the overall leader in the gross (172) by one shot, the net (138) by five strokes and the stableford by five points.