Stairmand edged fellow Raglan surfer Luke Hughes with a score of 18.17 to win his fifth title, while Williams (Whangamata) won her first national open women's title with a 13.5 score.
It was Stairmand's third straight win, which enabled him to join Wayne Parkes and Iain Buchanan, both of Auckland, in the record books with five titles.
His win also marked the first time someone has won the men's open title three straight years since Buchanan did it in 1987.
The day got off to a slow start as competitors waited for the building swell. But by 10:30am, conditions were contestable and the swell increased to 2m by the time the premier finals were held late in the afternoon.
Stairmand is renowned for lifting for finals, and found himself trailing Hughes early in the 30-minute final. Hughes' lead, which included scores of 8.4 and 8.0 out of a possible 10 points, was no issue for Stairmand as he built his scores with an 8.77, a 9.13 and a 9.03 to take the lead.
That left Hughes needing a near perfect 9.58 point ride for victory.‘‘Starting the year off with a win is always good and to have my name on that trophy with all those amazing surfers like Al Byrne, Wayne Parkes, Iain Buchanan, Maz and Jay Quinn is crazy,'' Stairmand said.
‘‘I am stoked to win any day, but nationals is always amazing. Hughesy kept me on my feet at the start. He is my shaper and I couldn't let him win. But he started off with two eight-point rides and I knew I had to step it up.
‘‘The waves just kept on pumping and pumping and I am just so stoked the waves were good for our final and let me have the opportunity to show my best surfing and eventually win.''
Maz Quinn (Gisborne), who was also chasing a fifth title, finished third, while Dunedin's JC Susan was fourth. Williams, who celebrated her 21st birthday on Wednesday, said she had dreamed of winning the national title since she was 7.
She had to fight hard for her maiden win, after taking a left early in the final and getting stuck on the inside.
‘‘It was pumping today,'' she said.
‘‘It was good to have such good waves for a comp. We all got a good opportunity and luckily it was a 30-minute final for me and that gave me time to secure the win.''
Williams, who won the junior world championship in 2011, will head to Australia at the end of the month for the start of the world qualifying series.
Fifteen-year-old Kea Smith, of Mount Maunganui, was second with an 11.1 score. Dunedin's Elliot Brown won the under-18 boys division after coming out on top in a closely contested final.
Just 2.5 points separated the four finalists, but Brown's 12.5 was good enough to come out on top.
‘‘I am so happy ... it means so much to me,'' Brown said.
‘‘I didn't make the 16s final, so to make this final and win, it is even better.''
Brown started with a score of 7.70, and knew he only needed a small score to move in to first. But he had to wait until the last minute of the final to snatch victory from Christchurch's Sam Sands.
Dunedin's Felix Dickson (men's 28-plus) and Tash Civil (senior women) also recorded wins, helping the South Coast Boardriders Association win the club championship over defending champion Bay Boardriders.
