At around midnight, the victim, a man in his 20, was at a party at Valley View Plot, Lockmeadow Farm, off the A422 Stratford Road, when three uninvited male guests attended and asked for him by name.
The men briefly left before returning with weapons and assaulted the victim, before leaving.
He received stab wounds to his abdomen and arm and was taken to hospital for further treatment.
The offenders are described as wearing balaclavas, jogging bottoms and hoodies and were using an approximately five-year-old Mercedes saloon-type car.
The victim is still in hospital in a stable and serious condition.
Speaking yesterday, Sunday, Detective Sergeant Simon Nelmes, from Thames Valley Police, said: “We believe that this was a targeted attack, and not random.
“I am appealing for any witnesses or anyone with information about this incident to please get in touch.
“If you have any CCTV footage in the area or any dash-cam footage if you were in the area around the time, I’d also ask that you check any recordings in case it has captured something that could assist our investigation.
“To contact us, call 101 or make a report on our website, quoting reference number 43220197866.
“Alternatively, you can provide information anonymously to the independent charity Crimestoppers, by calling 0800 555 111 or via its website.
“There will be a lot of police activity around Lockmeadow Farm today while officers investigate the incident.
“Please speak to any uniformed officers if you have any concerns or questions.”