After Tom Holmes' own goal gave the young Magpies a narrow lead at Adams Park, United's hopes of back-to-back shut-outs looked to be a difficult task as Reading were awarded a penalty late on.
However, Harker stood tall to produce a smart stop, guessing the correct way to push Josh Barrett's low driven spot-kick away from danger before the goalkeeper was then quickly forced into making another terrific save, tipping a dangerous half volley over his crossbar to maintain his clean sheet.
Substitute Tyrique Bartlett went on to seal United's win, bundling his rebounded shot into an empty net and, with Ben Dawson's side forced to work hard for their important victory, Harker believed achieving maximum points was down to a full team effort rather than his late minutes of marvellous goalkeeping.
"It wasn't the prettiest victory we've had this season," Harker told nufc.co.uk. "We've had less possession and chances than our opponents but we really dug deep and stuck together as a team.
"We got going in the first half and they didn't have many great chances but I think, overall, it's one of those scrappy victories that we all got through together.
"We knew the first goal could've been the winner for either team. We only had certain spells in the game so taking our chances was really important. I know Kell (Watts) was trying to claim the first goal but it wasn't - trust me!"
After Mo Sangare was adjudged to handle the ball inside the penalty area, Harker was heavily relied upon in the dying stages to maintain United's lead, including shortly after the penalty save, and revealed he was adamant on keeping Reading at bay.
"I thought it wasn't a penalty," Harker added. "It may have hit his hand but they were by his sides and there is nothing you can really do to get out of the way. Normally, I step back on my line and watch if the striker gives anything away.
"We watched a video on one of their penalty takers before the game but it wasn't that player who took it so it was goalkeeping instinct and I always thought I'd have a good chance of stopping the strike if I went the right way.
"They were pressing forward and, after saving a penalty in the 89th minute, there's not a chance you are going to concede in the 90th! The forward hit his effort at goal really well and I thought, for a moment, he'd put the ball over my head but I managed to give everything I've got left in the tank to get up and tip it over the bar."
With a Premier League 2 division two play-off spot firmly in sight, United lie two points adrift of third-placed Reading, with a game in hand over their counterparts.
Following an impressive 3-0 victory over Southampton in last week's Premier League Cup tie, the young goalkeeper kept his first back-to-back clean sheets for Newcastle's second string this term.
"It's a massive victory as it closes the gap to the teams above us," Harker added. "They (Reading) were five points ahead of Newcastle before the game so the win helps to push them towards the back end of the season while making it more comfortable if we want to get into the play-offs.
"Last week, I managed to pick up a clean sheet against Southampton on a very windy night but I didn't have a save to make all game. Against Reading, it was a lot different where I had to make a few more saves and work harder but that shows everything is done as a team."
