The 16-year-old from Southampton was arrested on suspicion of attempted murder.
An investigation was launched after five boys were stabbed just after 10.30pm.
Police said an uninvited group jumped a garden fence before seriously assaulting the victims – three who are aged 16 and two aged 17 – there and in surrounding streets.
Four of the boys suffered serious injuries and have now been discharged from hospital. The fifth, aged 17, remains in hospital in a life-threatening condition.
Officers have also been granted an additional 36 hours to question a 16-year-old and 17-year-old, both from Southampton.
The pair were arrested on suspicion of attempted murder on Monday morning.
Meanwhile, a 16-year-old boy from Bristol also remains in police custody, having been arrested on suspicion of attempted murder on Monday night.
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Police said officers had carried out searches at three addresses linked to those arrested, two in Southampton and one in Bristol, as part of ongoing enquiries.
They added several items were seized from those properties, without providing further detail.
