The Stormers maintained their unbeaten start to Super Rugby and inflicted the Chiefs first defeat with a 34-26 win in Cape Town on Saturday.
The Chiefs beat the Stormers 60-21 in the first stage of last season's playoffs but memories of that defeat were partly expunged as the Chiefs became the first New Zealand team to lose this year to a team from another conference.
Tries to Sikhumbuzo Notshe, Siya Kolisi, and Robert du Preez put the Stormers ahead 24-18 after a first half in which they dominated possession.
The Chiefs stayed in the match with several examples of backline brilliance, including a 95-meter attack which led to the first of two tries to winger Toni Pulu.
The Stormers produced a brilliant moment of their own to create a try for SP Marais, who also kicked two long-range penalties on either side of halftime.
The Chiefs struck back with a try to James Lowe but couldn't break down the Stormers' defense in the final quarter.
The seventh round also saw Japan's Sunwolves achieve an historic 21-20 win in Tokyo over South Africa's Bulls. The win, clinched by a 74th-minute penalty to Yu Tamura, was the Sunwolves' first of the season and only their second since they entered Super Rugby last year.
Travis Ismaiel scored a try in the 64th, converted by Tiaan Schoeman to give the Bulls a 20-11 lead. But the hosts responded six minutes later on a try by Takaaki Nakazuru that was converted by Tamura to cut the lead to 20-18.
Argentina's Jaguares came to the end of a three-match winning streak when they were beaten by the Sharks 18-13 in Durban.
Curwin Bosch kicked a late penalty to clinch the win in a close fought match which saw the Sharks lead 8-6 at halftime.
Earlier in Dunedin, flyhalf Marty Banks kicked 16 points as the Highlanders overshadowed Sonny Bill Williams' return to Super Rugby with a 26-20 win over the Auckland-based Blues.
Banks kicked six goals from six attempts to help the Highlanders recover from a 20-13 deficit at halftime to beat the Blues for the second time this season after their 16-12 win in round three.
Williams took the field in the 54th minute for his first appearance since he was forced out of the Rio de Janeiro Olympic sevens with an Achilles tendon injury. Only a minute earlier, Banks landed his third goal to give the Highlanders their first lead in the match at 23-20.
Williams made one threatening break, snuffed out by the Highlanders' defense, but in the 71st made a major passing error which allowed the Highlanders to carry the ball the length of the field and set up Banks' last penalty.
That goal gave the Highlanders their final six-point margin and forced the Blues, in the last nine minutes, to chase the converted try they needed to snatch victory. The Highlanders' defense was up to the challenge and the Blues' fourth loss in seven matches kept them at the bottom of the New Zealand conference.
In an all-Australian conference match, the ACT Brumbies scored 33 unanswered points in the second half to beat the Queensland Reds 43-10.
The win, the Brumbies' 10th in a row over Queensland, moved ACT eight points clear of the New South Wales Waratahs, who lost to the Hurricanes 38-28 in Wellington on Friday.