There were two nail-biting finishes, with Nigel Wright (Leith) beating Dan Delany (Auckland) 25-24 and Bill Clements (Alexandra) downing Andrew Kelly (Canterbury) 25-24.
Both games in the Speight's-sponsored event were won on the last bowl after see-sawing games.
The other Otago semifinalist was Shaun Scott (North East Valley), who beat Shayne Sincock (Canterbury) 25-14.
The only non-Otago semifinalist is Glen McDonald (Canterbury), who downed former World Bowls representative Paul Girdler (Dunedin) 25-18.
The most important win in Wright's 25-year bowls career came over Delany, who had been the form player of the event and was unbeaten in his seven section games.
"I'm excited," Wright told the Otago Daily Times after the game.
"I believe anyone in the top four has a chance to win tomorrow."
Wright was always playing catch-up bowls as the confident Delany looked to be in control.
Delany started strongly and led 13-3 after 10 ends, 17-8 after 15 and 22-15 after 21.
Wright finally secured control by scoring 10 shots on the last seven ends, including a four on the 26th end to draw level at 23-23.
Delany had a chance to win the game on the penultimate end but he was short with the bonus shot.
Wright walked down and studied the head before he played the winning bowl.
"There was a big swing on the head and I was not sure how it would break with the wind behind it," Wright said.
"It was not until the bowl fell over that I knew that I had the shot."
Clements, competing in the North East Valley singles for the third time, continued the form that won him his 52nd Central Otago title last season.
Kelly, a member of the New Zealand Commonwealth Games squad, held the winning shot before Clements played his last bowl.
It was a masterful shot that trailed the jack back to his own back bowls and he had two shots and advanced to the semifinals for the first time.
Kelly played aggressively and was lethal with his drives early in the game and sped to a 14-5 lead after 13 ends.
Clements then took control and scored 16 points on the next eight ends to lead 21-16.
Kelly came back to level the scores at 21-21 after 26 ends and drove the jack into the ditch two ends later to take three shots and lead 24-23 before the final end.
Scott, who finished runner-up last year, was always in control and had a comfortable win against Sincock.
He is confident about today's games.
"Sure I can do it," Scott said.
"I'm not here to muck around."
McDonald, a former New Zealand representative, has reached the semifinals for the third time.
He took the lead on the eighth end and had control after that and won the game with a four on the 23rd end.
Scott will play McDonald and Wright will face Clements in this morning's semifinals.
Play starts at 9.30am, and the final is expected to start at 1.15pm.
