DUNEDIN, New Zealand — The Waikato Chiefs began their defense of the Super 15 rugby title Friday with a 41-27, bonus point win over the Otago Highlanders in a match which saw six lead changes. Lightweight center Tim Nanai-Williams used his exceptional pace to score the first and last of the Chiefs' four tries as spectacular backline action enlivened the first match of the season in the New Zealand conference. The teams exchanged tries — seven in total — as play swept from one end to the other of Dunedin's enclosed stadium. At its most frenetic, two tries and 15 points were scored as the lead changed hands three times in three minutes immediately after halftime. Brumbies beat Rebels In Melbourne, Brumbies fullback Jesse Mogg scored a try and set up Clyde Rathbone's first five-pointer since returning from a four-year break Friday as the ACT also earned a bonus point in a 30-13 win at the Melbourne Rebels in the Super 15 rugby. The Rebels led 13-12 at halftime but were starved of possession after the break, allowing the Brumbies to dominate with 18 unanswered points. Mogg opened the scoring in the fourth minute after Melbourne flyhalf Kurtley Beale turned over the ball when he was tackled midfield. Mogg then set up the Brumbies' second try for winger Rathbone. Fullback James O'Connor set up the Rebels only try for Scott Higginbotham in the 18th minute and added two conversion and two penalties to give the home side the lead at the break. The second half belonged to the Brumbies as captain Ben Mowen crossed in the 61st minute and substitute Robbie Coleman scored the fourth try for a bonus point in the 74th. Center Christian Lealiifano contributed two conversions and two penalties for the visitors. The Rebels' woes were compounded by fitness concerns for their two star backs. O'Connor had a suspected concussion while Beale injured a shoulder while making a tackle. The Brumbies are now undefeated from two rounds after having downed the Queensland Reds 24-6 in their opening match last week. — Agencies