PRETORIA, SOUTH AFRICA - MARCH 22: Marcell Coetzee of the Sharks tackled by Jacques du Plessis of the Bulls during the Super Rugby match between Vodacom Bulls and Cell C Sharks at Loftus Versfeld on March 22, 2014 in Pretoria, South Africa. (Photo by Lee Warren/Gallo Images)

Sydney – The Sharks and defending champions Waikato Chiefs crashed to their first defeats of the Super 15 season as the title race tightened up in all three conferences this weekend.

The Sharks fell 23-19 to the Northern Bulls in a South African derby in Pretoria, ending their run of four wins.

The Durban-based outfit's overall lead was cut to just two points from Australia's ACT Brumbies after the Chiefs were upset 18-15 by the rejuvenated Western Force in Perth.

It was the two-time champion Chiefs' first loss of the campaign and a setback before embarking on their two-match tour to South Africa, starting with the Bulls next Saturday.

The Golden Lions closed to within three points of the Sharks in the South Africa conference and fourth overall after a 23-20 home victory over Australia's Queensland Reds.

The Brumbies leapfrogged the NSW Waratahs to the top of the Australian conference with a 25-15 win over South Africa's Western Stormers, after the Waratahs scored a 32-8 bonus-point win over the Melbourne Rebels.

The Blues kept in touch with the top-six playoff spots in a high-scoring 40-30 win over South Africa's Central Cheetahs in Auckland.

In the weekend's remaining game, the Otago Highlanders edged fellow Kiwis the Wellington Hurricanes 35-31 in Dunedin.

Legendary lock Victor Matfield marked his return as captain by leading the Bulls to a a thrilling victory over the Sharks.

Matfield, the second most-capped Springbok with 110 Tests, ended a two-year retirement to play for the Pretoria outfit.

Matfield was dominant at the lineout as the home side scored two second-half tries to turn a 13-6 half-time deficit into a four-point triumph at Loftus Versfeld.

Rejuvenated Western Force continued their giant-killing run by stunning titleholders Waikato, scoring the only two tries of the match and then holding firm in a pulsating finish.

It was the Force's third straight win for the first time since 2007 and only the second time in their history, and marked just their second victory in eight encounters with the powerful Chiefs.

They ended Waikato's unbeaten run this season and it was the first time the New Zealanders had been held tryless in Australia in Super Rugby since 2001.

In Canberra, winger Robbie Coleman scored two of the Brumbies' three tries to edge a tight match against the Stormers.

The Brumbies hung on despite Stormers' substitute back Juan De Jongh crashing over for a 75th-minute try to cut the deficit to three points, with fly-half Peter Grant missing two relatively easy kicks in the final stages.

A late Courtnall Skosan try allowed the Lions to snatch a win over the Reds in a thriller at Ellis Park.

But the South Africans had to endure an agonising wait before the television match official and referee confirmed that the score stood, amid suspicions of a double-movement.

The Lions trailed by 17 points late in the first-half but the Australians, beaten by the Sharks in Durban last weekend, contributed to their downfall with ill discipline that led to two players being sin-binned during the closing stages.

Israel Folau scored two tries and Kurtley Beale ran the show as the Waratahs claimed a four-try bonus-point win over the Rebels in Sydney.

Wallaby fullback Folau has now scored eight tries in four matches in this year's Super Rugby competition and he owed both his tries Friday to Beale's playmaking skills.

The Blues held off the late-charging Cheetahs in a bonus-point victory in their first home game after a fruitless trip to South Africa.

The Highlanders defied a late fightback from the Hurricanes to win by four points. Wellington scored three tries to two but Lima Sopoaga guided Otago to victory by kicking nine goals from 10 attempts. – Sapa-AFP