Slade's try in the 51st minute and his two conversions and two penalties helped clinch the Dunedin-based Highlanders' first win of the season. The contest also marked the 100th Super Rugby appearance of lock Brad Thorn, who ended the match in the sin-bin.
A match which contained an abundance of scrappy play, errors and tactical misjudgements from both teams also included a handful of brilliant tries and a thrilling finish as the Highlanders, down to 14 men, defended desperately on their line.
VIDEO: Highlanders v Sharks, highlights
Slade's try was the last scoring play by the Highlanders, giving them a 25-15 lead with 25 minutes left. When centre Meyer Bosman scored his second try of the night for the Sharks, slashing the lead to 25-22, the Highlanders' winless run to the season look liked it might be extended.
They defended with outstanding commitment throughout the last 20 minutes of the match, mostly situated on their own line and finally with only 14 men as the 38-year-old Thorn watched on from the sidelines.
The Sharks attacked relentlessly in the last 10 minutes, often carrying the ball for more than 20 phases within 10m of the line. The Highlanders repelled one such attack in the 78th minute, finally forcing a turnover on the 25th phase but managing only to clear the ball to touch.
The Sharks received a steady torrent of penalties late in the match. From one, in the 79th minute, Thorn was sin-binned for a professional foul.
Late in stoppage time, Highlanders winger Hosea Gear made a crunching tackle to force a turnover and allow his team, buckling under pressure but unbowed, to win possession and stop the clock.
Born only a few miles from the stadium at which the match was played, Thorn made his name first as an Australian rugby league international before becoming an All Black. He has made only eight appearances for the Highlanders with his previous 92 Super Rugby matches, between 2001 and 2011, coming in the colours of the Christchurch-based Crusaders.
"First of all, I take my hat off to the Sharks who gave a terrific performance a long way from home," Thorn said. "I'm just really honoured to come back to where I'm from and I'm very, very proud to play in front of my people."
The match see-sawed throughout. Centre Shaun Treeby, returning from injury, scored the home team's opening try in the 10th minute. But Bosman's first try and a superb counter-attacking effort from Lwazi Mvovo put the Sharks 15-7 ahead at half-time.
Slade hit the post twice with penalty attempts, but his try and another by scrumhalf Aaron Smith gave the Highlanders a 10-point lead midway through the second half. The Sharks hit back through Bosman's second try 19 minutes from fulltime before their late, unsuccessful push.
Scorers:Highlanders:
Tries: Shaun Treeby, Aaron Smith, Colin Slade
Conversions: Slade (2)
Penalties: Slade (2)
Sharks:
Tries: Meyer Bosman (2), Lwazi Mvovo
Conversions: Patrick Lambie (2)
Penalty: Lambie
Teams:
Highlanders:
15. Ben Smith, 14. Phil Burleigh, 13. Tamati Ellison, 12. Shaun Treeby, 11. Hosea Gear, 10. Colin Slade, 9. Aaron Smith, 8. TJ Ioane, 7. John Hardie, 6. Jarrad Hoeata, 5. Josh Bekhuis, 4. Brad Thorn, 3. Chris King, 2. Andrew Hore (captain), 1. Tony Woodcock
Substitutes: 16. Liam Coltman, 17. Ma’afu Fia, 18. Elliot Dixon, 19. Joe Wheeler, 20. Fumiaka Tanaka, 21. Hayden Parker, 22. Jason Emery
Sharks:
15. Riaan Viljoen, 14. JP Pietersen, 13. Francois Steyn, 12. Meyer Bosman, 11. Lwazi Mvovo, 10. Patrick Lambie, 9. Charl McLeod, 8. Lubabalo Mtembu, 7. Marcell Coetzee, 6. Keegan Daniel (captain), 5. Franco van der Merwe, 4. Pieter-Steph du Toit, 3. Jannie du Plessis, 2. Kyle Cooper, 1. Wiehahn Herbst
Substitutes: 16. Craig Burden, 17. JC Janse van Rensburg, 18. Anton Bresler, 19. Jean Deysel, 20. Tian Meyer, 21. Piet Lindeque, 22. Odwa Ndungane