The side, which won the title in 2015 and 2016, lost to an impressive Tupapa Maraerenga Matie Bar 5-19 at a slippery BCI Stadium ground in Nikao.
Tabusoro, the Fijian community team mostly made up of players based in Rarotonga and New Zealand, lacked the firepower to shoot down the skillful Tupapa.
Tupapa made a brilliant start to their campaign after thrashing Avatiu Blue 49-0 in its opening pool match on Thursday.
The side heads into today’s Cup quarter-final as the top team from Pool A.
Tabusoro had to beat Avatiu Blues in their final match last night to make it through to the Cup quarters.
In Pool B, Avatiu Gold recorded close wins over Atiu Warriors 19-12 and Arorangi Boys 7-5 to finish on top.
The Clive Nicholas-coached side, which finished runners-up in the past two tournaments, is hoping to go up a notch and win the 2017 Raro Rugby Sevens title.
The former All Black Zac Guildford-led Tauae Bulls have been in an impressive form in Pool C, winning all their group matches.
The side defeated the national development squad Manatoa 27-0 in their opening pool match before thumping Veiyasana Vikings 43-0 and N8Tive Rebels 22-0.
Yalovata is the top gun in Pool D after winning its opening two pool matches against top seed Tupapa Maraerenga Panthers and TKV Reds.
The side defeated the Panthers 19-7 in its opening match on Thursday before downing the Reds 17-5 yesterday.
The standings of the pools in men’s competition were still undecided when this edition went to press last night, as some pool matches were underway.
Meanwhile in the women’s competition, defending champions Vaine Toa - Raro All Stars finished the preliminary round unbeaten after three wins.
In their opening match, the side thumped Cookies & Cream 34-0 on Thursday before overcoming Wellington Barbarians 12-10 and TKV Hot Mix 29-0 yesterday.
The Raro All Stars head into today’s semi-final against the TKV Hot Mix as the firm favourites while the Barbarians are the top bet against the Cookies & Cream in the other semis.
Today’s competition will kick off at 11am with the men’s Bowl quarter-finals. The main final (men’s Cup) is scheduled for 6pm.
Day One – TKV Hot Mix 0 Wellington Barbarians 49, Raro All Stars 34 Cookies & Cream 0, Avatiu Blues 0 Tupapa Panthers 49, Arorangi Cowboys 14 Atiu 14, N8tive Rebels 27 Vikings 7, TKV Reds 5 Kotaa Gliders 21, Tupapa Centre 7 Yalovata 19, Tauae Bulls 27 Manatoa 0
Day Two – Cookies & Cream 27 TKV Hot Mix 0, Vaine Toa - Raro All Stars 12 Wellington Barbarians 10, Tauae Bulls 43 Veiyasana Vikings 0, Tupapa Maraerenga Panthers 21 Kotaa Gliders 17, Tabusoro 5 Tupapa Maraerenga Matie Bar 19, Avatiu Gold 19 Atiu Warriors 12, Manatoa 17 N8tive Rebels 10, Yalovata 17 TKV Reds 5, Wellington Barbarians 29 Cookies & Cream 5, Vaine Toa - Raro All Stars 29 TKV Hot Mix 0, U17 Tahiti Team 0 U17 Cook Islands Team 27, Avatiu Gold 7 Arorangi Cowboys 5