The Robins produced an excellent display at Summerleaze to win 3-1 and end Port's four-match winning run.
The game marked a return for goalkeeper Martin Hutt, who took over from the injured Chris Adams.
Dan Sleet hit the bar on 17 minutes and moments later Gary Newson scored from new signing Adam Pharo's cross.
Ben Knight made it 2-0 on 48 minutes from a penalty he earned before Harry Swabey gave the Robins their third, again from the spot after Holyport's Matt Rolfe had pulled one back on 77 minutes.
Port also had a man sent off after a moment of madness from the frustrated James Flint.
Binfield completely over-ran Shrivenham to win 6-0 away from home. Carl Davies, Danny Wing (pen) and Ian Davies all scored in the first- half.
The Moles continued their rout with three goals in the last 11 minutes from Callum Whitty and a brace from James Suarez. They were due to play Witney Town at Hill Farm Lane on Monday night.
Wokingham & Emmbrook moved into the next round of the League Challenge Cup with a 4-1 win over Hellenic Division One West side Winterbourne Utd.
Matt Jones, making his first start since moving from Finchampstead, made an immediate impact, heading in the opening goal after 25 minutes.
The visitors hit back 10 minutes later but it was soon cancelled out by Danny Horscroft's strike.
The influential Jones then set up Horscroft for his second of the game shortly before the hour and Garry Sargeant wrapped things up in the 68th minute.
Satsumas' Alex Luis also missed a penalty late on.
Finchampstead were too strong for Didcot Town Reserves in Division One East, with Chris Hollis netting a pair either side of the break and Dan Williams grabbing another in a comfortable 3-0 win.
A late rally from Sandhurst Town could not stop them from an entertaining 4-3 defeat to Windsor in Combined Counties Premier.
The Fizzers conceded three times in the opening half an hour with Yashwa Romeo (2) and Chris Ellis doing the damage for the visitors.
Steven Eyango Bwanga pulled a goal back on 43 minutes to make it 3-1 at half- time but Windsor's Kyle Anthony made it 4-1 on 70 minutes.
Goals from Chris Fermie and Liam Eagle late on made for a nervy finish but Windsor held on for the victory.
Eversley reached the second round of the League Cup with a 2-1 victory over Worcester Park.
Having gone a goal behind early on, the Boars then equalised on the half hour after Matt Stamp's shot was deflected in by a Worcester Park defender. It was Stamp again who put the Boars 2-1 up with a neat finish.
For full reports and pictures pick up the News on Thursday.