The Hammers secured a 1-0 win at St James' Park on Sunday to move up to sixth place in the Barclays Premier League table.
Senegal international Diame, 25, moved to Upton Park from Wigan on a free transfer in the summer and believes the win at Newcastle stands out in the recent run of good form from Sam Allardyce's side.
"It was a fantastic result against Newcastle, probably the best since I joined the club, and we worked very hard for the three points," he told the club's official website.
"The manager gave me a lot of confidence going into the game so I tried to give it back on the pitch and I think I did a good job."
Diame was one of a number of players brought in by Allardyce following success in the play-off final last year, with the likes of Andy Carroll, Matt Jarvis and Yossi Benayoun also joining the Hammers.
Despite offers from abroad, Diame highlighted the marquee signings made by Allardyce helped him choose West Ham as his new club when his contract at Wigan expired.
He said: "That is why I came here. When I spoke to the club I knew they were trying to build a very good team. We are working very hard every day on the training ground and you can see it is paying off.
"People did say 'Why are you going to West Ham when you can play in the Champions League?' but they can see why I did now.
"It is a very big club in England and I am very happy to be here, now I am hoping that our good performances will continue."