Team Bath beat Surrey Storm and Loughborough Lightning overcame London Pulse to secure semi-final spots in the Superleague.
Strathclyde Sirens came from 22-19 down at half-time to stun Wasps 44-39 and breathe life into the top-four race.
Saracens Mavericks lost 60-42 to third-placed Manchester Thunder, allowing Leeds Rhinos - who beat Severn Stars - and Sirens to leapfrog them.
Six points separate fourth and seventh with four rounds to be played.
Bath's 55-39 victory over second-from-bottom Storm was their 15th of the season, while Lightning's 42-35 win over Pulse keeps them three points behind - with sights now set firmly on the finals weekend at the end of June.
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Game of the week - Wasps 39-44 Strathclyde Sirens
With Sirens continuing to improve this season, pressure has continued to mount on Wasps' campaign for fourth spot.
The game went goal-for-goal for the first-half until Wasps edged a half-time advantage. Veteran Wasps shooter Rachel Dunn was prolific under the post, scoring her 450th goal of the season, but Sirens captain Gia Abernethy drove through mid-court to soak up the pressure and keep her side's score ticking over.
A devastating third quarter for Wasps proved to be their undoing. They lost mid-courter Iona Christian to an ankle injury and failed to prevent killer passes into the Sirens shooters, with the two-time champions eventually succumbing to the Scottish outfit's persistence.
Wasps head coach Mel Mansfield said the defeat had put them in a "difficult position" and that the 16-6 third-quarter deficit had been "unforgivable".
The race for the top four
Bath and Lightning have confirmed their semi-final spots and Thunder are expected to join them - but the fight for the last spot could go the distance.
Wasps seemed to be in control, but a lack of consistency has left them clinging on.
After Sunday's defeat by Sirens, Wasps then lost 53-47 to defending champions and great rivals Thunder on Monday to be left in a precarious position. They have only two games left, having played more than any other team.
Mavericks, the only side to have beaten league leaders Bath, had looked set to disrupt the top-four and challenge for their first title since 2011 - but the loss to Thunder and success of teams around them means they drop to seventh, albeit with games in hand.
Sirens, who have eight wins and two draws, have muscled themselves into contention alongside Rhinos, who have impressed in their debut season with nine wins - two coming against Wasps and Mavericks.
The Superleague will return with a double-header weekend from Friday, 28 May.
Results & fixtures
Sunday, 16 May
Severn Stars 36-63 Leeds Rhinos
Team Bath 55-39 Surrey Storm
Wasps 39-44 Strathclyde Sirens
Manchester Thunder 60-42 Saracens Mavericks
Monday, 17 May
Wasps 47-53 Manchester Thunder
London Pulse 35-42 Loughborough Lightning
|Vitality Netball Superleague table 2021|