Against Nelson, Whanganui were embarrassed to be dismissed in the 15th over for 44, with Nelson bowlers Jared McKay (4-17) and Ben Hazlett (3-18) ripping them apart.
While Whanganui picked up three wickets, two by their Active Physio Wanganui senior player Sam Beard (2-23), Nelson reached 46-3 in the 14th over.
Wairarapa were likely confident, therefore, when Whanganui put them into bat and they amassed 217 before being bowled out in the 45th over.
Kelsey Fahey (78) and Jack Forrester (55) had the key partnership, while Whanganui's best bowlers of the eight used were O'Leary (3-21) and Matthew Simes (3-45).
But this time, Wanganui were focused with the bat and reached their target on the third ball of the final over.
Simes with 67 not out from 125 balls and captain Angus Dinwiddie, of Collegiate, with 69 from 99 balls, held their nerve, and then O'Leary scored 26 from 27 balls to see it home.
The team then went on to face Manawatu and won by eight runs in a low scoring thriller.
Bowled out for 108 with only Dinwiddie (33) and opener Liam Fowler (21) making a dent in Manawatu's bowling, which included Ben O'Connor picking up 4-22, Whanganui's own bowlers refused to give up.
Beard (1-25) tied Manawatu down early and O'Leary was outstanding with 5-23, destroying the top order.
Thomas Walshe (41no) tried to carry the tail through with him, but James Pennefather (2-30) and the other bowlers finished off what O'Leary started by the 39th over.
Despite the good comeback, Whanganui missed the final as Manawatu went through on a higher run rate.
They took it out on Hawke's Bay yesterday, collapsing them to 59-9 with Pennefather getting five wickets and O'Leary picking up four.
Whanganui would go on to dismiss the home side and defeat them handily.
"Connor O'leary and Sam Beard provided the bowling foundations to bring down Manawatu," said manager Dilan Raj.
"Coach Hayden Pudney has gelled the unit into a tight team that is starting to have a lot belief in their team and individual ability."
Meanwhile the Watson Wanganui Under-15 team was in a tough two-day fight with Manawatu yesterday.
The team started their tournament with great success, beating Marlborough U15 by 10 wickets.
Bowling them out for 32 with Hadleigh O'Leary picking up 5-6 within six overs, Whanganui made 135-5 declared on the back of Sam Sherriff (33) and Cameron McIntosh (39).
They then hunted an innings win, just missing it when Marlborough got through to 110 in their second innings, leaving Whanganui only eight runs to chase for victory.
Charlie Greatbatch (3-19), Sherriff (3-19) and Ben Kelt (2-29) did the main damage with the ball in Marlborough's second dig.
It was tougher stuff with Manawatu, who made 133 in their first innings and then bowled Whanganui out for 62.
Kelt (3-13) and Beau Hourigan (3-26) did well with the ball for Whanganui, but no one really got going with the bat, with Kelt's 19 being the highest score.
Manawatu then went back out and reached 159-7 declared, led by Campbell Ingram's excellent 60 not out, while Charlie Greatbatch (2-28) was the best of the bowlers.
Set a tough 230 to win, Whanganui were sitting on 121-7 at press time.
