Spaniard Jose Antonio Reyes provided the crucial goal as Arsenal moved a step closer to recording their own piece of Premiership history, but only after a mighty fright on the South Coast.
Reyes repaid a huge slice of his Â£17million fee following his January move from Sevilla when he fired Arsenal level five minutes into the second half to extend their unbeaten run to 36 matches.
The Spanish striker showed supreme confidence and sublime skill to send the first-time shot low into the bottom right-hand corner after Portsmouth could only partially clear Thierry Henry's corner from the left.
The result leaves just Fulham and Leicester standing in the way of Arsene Wenger's side going the entire 38-game programme without defeat, but they were made to fight all the way by in-form Pompey who extended their own unbeaten run to eight games in the process.
Two months ago Pompey were facing the very real threat of immediate relegation back to the First Division, but five wins from seven games had taken them to Premiership safety and they showed their new found confidence by taking the game to the newly crowned Premiership champions.
Strike duo Lomana LuaLua and Yakubu Ayegbeni had already gone close in the opening quarter of an hour before the latter shocked the Gunners by firing the home side in front on the half-hour mark.
Defender Kolo Toure failed to deal with a long ball forward from Matthew Taylor allowing the Nigerian to nip in and fire a low shot in on goal from a tight angle.
German goalkeeper Jens Lehmann could only partially block the shot while centre-back Sol Campbell despairingly failed to stop the ball crossing the line.
Reyes was unlucky not to have opened the scoring a minute before Yakubu's opener when his 25-yard drive was deflected on to the crossbar while Pompey goalkeeper Shaka Hislop did brilliantly to deny Henry when he was clear through on goal in the 33rd minute.
Henry was again thwarted by the outstanding Hislop a minute before Reyes' equaliser when his sidefoot shot was tipped on to the crossbar from just ten yards out after good build-up play from Freddie Ljungberg.
Arsenal pressed forward in search of a second goal after pulling themselves level with Henry going close on two other occasions, but it was Portsmouth who had the best chances to win an entertaining encounter.
Lehmann preformed heroics to deny Yakubu a second goal on 78 minutes when the striker had just the German to beat following LuaLua's neat flick on.
Then Arsenal's goalkeeper again showed his agility to save Dejan Stefanovic's free-kick from 25 yards out three minutes later.