Smith scored 18 points on the front nine and 20 on the back nine for a total of 38 stable-ford to emerge tops in the tournament that attracted 131 golfers.
Salim Tweshe (37) was the runner-up to relegate handicap 14 golfer Rohit Devani who carded 18 on the first nine and 19 on the second, to third on count back.
Devani won the honour of being the nearest to the pin with 6ft 11 inches to cover in Saturday’s tournament.
Handicap 7 lady golfer, Diana Munyao scored 36 for victory ahead of Jayne Githere who carded 36. In the guest category, Stephano Messina emerged best with 34 beating Richard Githii (handicap 18) by three strokes.
The staff prize was scooped by Tim Gitonga playing off handicap 27. Gitonga managed 14 on the front nine and 18 points on the back for a total of 32.
In the junior category Agil Ishaq topped with 34 points; (14, 20) where Kellen Weku playing off handicap 26 dominated the first nine with 19 while handicap 8 golfer Vishnu Dhutia was best in the second with 21.
The prize for the longest drive went to handicap 9 Taufiq Balala who managed a 420-yard drive on the 6509-yard course.
Nyali brought an end to the NIC Bank Series which visited nine regions including Eldoret Golf Club, Vet Lab Sports Club, Nanyuki Sports Club and Limuru Country Club in July.
In August, the series visited the Nyanza Club in Kisumu where golfers from Kakamega, Kisii, Kericho and Nandi Bears participated.
In September, the series moved to the Nakuru Golf Club, Kiambu Club and Thika Sports Club. It drew over 2,000 golfers from across the country.
Playing off scratch, the national team player returned 1 over par 289 after four rounds on the par-72 Thika Golf Club course.
Opati automatically claimed a place in the 2012 Kenya Open, a Challenge Tour professional golf event with the victory.
Opati started his campaign at Thika with a opening score of 1-under par 71, followed this with a 4-under par 68 to establish a 7-stroke lead that was narrowed down to four at the end of the third round.
Patrick Kingori, Joseph Karanja, Robinson Owiti and Justus Madoya failed to capitalize on Opati’s poor finishing round of 75 on day three by returning equally poor efforts.
Opati’s rounds of 71, 68, 75 and 75 for 1-over total of 289 may have been good for a 9-stroke victory and the Kenya Amateur Trophy, but failing to break par on a relatively easy golf course is damning for the standards of golf in Kenya.
Justus Madoya, Robinson Owiti, Joseph Karanja, Anthony Kinuthia and Patrick Kingori finished second on 10-over 298.
The Kenya Amateur Open is part of the Keringet sponsored KGU Golfer of the Year and is the most prestigious amateur championship in Kenya.
Three events now remain on the Keringet GOTY series; the Manchester Salver in Eldoret, the Uhuru Shield at Royal Nairobi and the season ender, the Nyali Open at the Nyali Golf and Country Club.
Keringet have committed to support the GOTY series for three years.