The defending champion Crusaders weathered a severe hailstorm and a stubborn showing by the winless Sunwolves to prevail 33-11 and improve their chances of a record-extending ninth Super Rugby title on Saturday.
The Melbourne Rebels' now fading hopes of a maiden title took a second blow in the space of a week when they went down to the Bulls 28-10.
Also, the Chiefs handed Queensland Reds their fourth straight loss and the Sharks finished strongest — in attack and then in last-gasp defense — to edge a tight South African derby against the Stormers 24-17.
ACT Brumbies will host the Jaguares on Sunday to close out week 10.
Whatever the result of that game, New Zealand's Crusaders will stay second overall in the standings halfway through the regular season, a point behind South Africa's Lions and with a game in hand.
The Christchurch-based Crusaders started as expected against Japan's struggling Sunwolves with a try in the first minute and another seven minutes later to lead 14-0.
But the Sunwolves hit back with a try, then the Crusaders' home stadium was hit by a serious thunderstorm which brought a torrent of hail.
For the next 40 minutes, on both sides of halftime, the Crusaders struggled to control the match as lightning flashed overhead.
The Sunwolves chipped away at the lead with penalties to New Zealand-born flyhalf Hayden Parker, closing to 14-11 and pressing the home team's line.
The Crusaders were finally able to generate some possession in the Sunwolves half and score two tries within five minutes to Ryan Crotty — his second of the match — and winger Manasa Mataele to gain a comfortable advantage and a bonus point. They finished with a try in the final minute to Jack Stratton on debut which made the winning margin flattering.
"The Sunwolves made us work for every point we got," Crusaders captain Matt Todd said. "The storm made it slippery, especially when the hail came down and we probably took too long to adjust."
The Rebels — early pacesetters this season — were out to bounce back from a surprise home loss to Argentina's Jaguares. They had to do it after trekking across South Africa to visit the Pretoria-based Bulls without their injured experienced scrumhalf and playmaker Will Genia.
Bulls hooker Adriaan Strauss scored on five minutes — the fifth try in three games for Super Rugby's most capped player — and the Rebels were never in a realistic position to win.
The Bulls added tries through center Jesse Kriel and wing Divan Rossouw for a 21-3 halftime lead.
Genia's replacement Michael Ruru, maybe the Rebels' best player on the day, finished off a slick handling move for the Rebels' only try early in the second half.
But Bulls replacement scrumhalf Andre Warner caught a tiring Rebels forward pack off-guard near the end with a quick tap from five meters out to seal the 28-10 win. The Rebels slipped to seventh in the standings.
A tight Sharks-Stormers game came to life with a try from each team just before and after halftime.
Stormers captain Siya Kolisi's rampaging run and looping inside pass put Raymond Rhule in for the first try and gave them a 7-3 halftime advantage.
Sharks center Lukhanyo Am enhanced his reputation as one of South Africa's best young backline talents by starting and finishing the move for the Sharks' first five-pointer two minutes into the second half.
The teams swapped tries again, to hooker Ramone Samuels for the Stormers and flanker Jean-Luc du Preez for the Sharks. At 17-17, front-rower Thomas du Toit supported a break to take an offload and force his way over for the game-clincher in the 73rd.
The Sharks repelled a Stormers surge on their try-line after the final hooter to cling on for only a second win this season, and a pride-saver after last weekend's 40-10 humiliation at home to the Bulls.
"After a disappointing week like last week we really wanted to stick together and tighten everything up and give a performance like we did," du Toit said.
Earlier, New Zealand's Chiefs beat the badly off-form Reds 36-12, with tries to Tyler Ardron, Charlie Ngatai and Brodie Retallick opening up a 24-0 halftime lead.
The Reds, who lost skipper James Slipper through injury in the first half, rallied to save face in the second, with Samu Kerevi scoring two tries. But a late Samisoni Taukei'aho score sealed a crucial Chiefs bonus point.