Both teams did stirring simultaneous haka before kickoff.
Timaru BHS will face a stern test next Tuesday against fellow unbeaten leaders and defending champs Christchurch BHS.
In other significant UC Championship results, Christ's and St Bede's both bounced back from first round losses to defeat, respectively, St Thomas 27-18 and Marlborough BC 38-14.
In the Otago premier colts club grade, Otago BHS First XV and Southland BHS suffered reverses, to Alhambra-Union and Dunedin respectively.
The Chiefs Cup kicked off with Hamilton BHS and Rotorua BHS flexing their muscles, while New Plymouth BHS, with a double to fullback Jamahl Hapi, beat Sir Francis Douglas Memorial 27-17 for Taranaki First XV bragging rights. Tauranga Boys' College narrowly beat 2016 Central North Island champions St Paul's Collegiate 23-20.
In North Harbour, Westlake BHS blanked Orewa 72-0, while Massey had to work hard to subdue Whangarei BHS 21-16. Rangitoto tipped over Rosmini 24-14.
In Auckland, Sacred Heart retained the Brother Maurice-Henry Cooper Cup with a tight 16-11 win over Auckland Grammar, prop Fatongia Paea scoring the sole try for the victors.
Tamaki and Liston suffered defeats in their first games back in 1A, though they were pleasingly competitive. King's' 34-12 result over De La Salle marks them as semifinal contenders.
In the Sanix unofficial world schools tournament in Japan, 2016 Auckland and New Zealand champions Mt Albert Grammar School were defeated 9-3 in last week's final by Lycee de la Borde Basse of Castres, France.
In general, with many of the class of 2016 having left, MAGS found the going tough, dropping one pool match and working hard to repel two Japanese schools in the playoffs. They will now have to swiftly get their heads back into the reality of Auckland 1A rugby when they travel to Dilworth on Saturday.
North Harbour 1A
Westlake BHS 72 Orewa 0
Takapuna Grammar 36 Birkenhead 5
Massey HS 21 Whangarei BHS 16
Rangitoto 24 Rosmini 14
Auckland 1A
Aorere 21 Tamaki 8
St Peter's 13 Kelston BHS 3
King's 34 De La Salle 12
Dilworth 27 Liston 13
Sacred Heart 16 Auckland Grammar 11
Auckland 1B
Tangaroa 32 Howick 8
Botany Downs 25 Avondale 5
Mt Roskill Grammar 27 Macleans 24
St Paul's 27 Otahuhu 3
Southern Cross 17 Mangere 13
One Tree Hill 44 Edgewater 0
Papatoetoe 22 Onehunga 8
Pakuranga 30 Waitakere 19
Chiefs Cup
Hamilton BHS 53 Manurewa HS 7
Rotorua BHS 41 St John's (Hamilton) 12
Tauranga BC 23 St Paul's Collegiate 20
New Plymouth BHS 27 Francis Douglas Memorial 17
Chiefs Trophy
Cambridge HS 52 Pukekohe 13
Taupo Nui a Tia 17 Rosehill 7
Chiefs Bowl
Paeroa 58 Waiuku 5
Bay of Plenty
(Division one)
Te Wharekura o Mauao 39 Aquinas 3
Rotorua BHS Second XV 19 Rotorua BHS Third XV 15
Trident HS 26 Tauranga BC Second XV 19
Hurricanes Tranzit Festival
Palmerston North BHS 22 St Pat's (Town) 18
Wellington 19 Gisborne BHS 13
Hastings BHS 46 Wairarapa 7
Napier BHS 22 Rongotai 8
UC Championship
Timaru BHS 43 (Dean Andrews 3, George Brown, Monty Nixon, Melvin Pauni, Maka Mafileo tries; Andrews 4 con) Shirley BHS 17 (Nathan Koolen, Vaysion Kara tries; Mitchell Barry 2 con, pen) HT: 31-10
Christchurch BHS 46 Burnside HS 8
Nelson 50 Lincoln Combined 6
St Andrew's 52 Roncalli Combined 19
St Bede's 38 Marlborough BC 14
Christ's 27 St Thomas 18
Rangiora HS 27 Waimea Combined 17
Otago
Mt Aspiring 29 Taieri 14
King's HS 54 Otago BHS Second XV 22
John McGlashan 35 South Otago 0
Dunstan HS 55 Kavanagh 5
(Otago premier club colts)
Alhambra-Union 24 Otago BHS First XV 19
Dunedin 59 Southland BHS First XV 20
Sanix tournament (Japan)
Quarter-final: MAGS 33 Tokai University Gyosei High School 19
Semifinal: MAGS 27 Higashi Fukuoka High School 12
Final: Lycee de la Borde Basse 9 MAGS 3
