The young defender, 20, stepped out for his full debut and Premier League bow in the cauldron of Upton Park for what is always a fiercely-contested derby.
But he appeared completely unfazed, partnering skipper Younes Kaboul in central defence before switching to right-back in a reshuffle after Kyle Naughton’s early red card.
And what was already an outstanding debut went into overdrive in the 93rd minute when he raced onto Harry Kane’s pass, skipped around goalkeeper Adrian and slotted home the winner.
“I was just really happy to play to be honest and to score on top of that, well, I never imagined it,” said Eric.
“We knew it was going to be hard 11 against 11 at West Ham so with the sending off it was even harder.
“I moved to right-back but I’d played there for Sporting (Lisbon) before, so I wasn’t completely in shock going to play there. I was just delighted to score at the end.”
Below: Eric's heat map shows where he spent most time on the pitch at West Ham - more stats in our Match Centre
So what was he thinking as Harry’s defence-splitting pass sent him through on goal?
“I saw the keeper coming out in the corner of my eye and I wanted to touch the ball around him and put it in. It all happened really quickly. I didn’t get any time to think about it and that was probably a good thing!
“I really enjoyed it and it’s why I wanted to come here, to play in games like this. I’m really happy to be here.”