The Black Cats breakthrough star says it is obvious how much more solid the side have become under the manager.
The Black Cats were in desperate relegation trouble for the majority of the season, spending more time in the bottom three than any other side including hopeless bottom side Aston Villa.
However, under Allardyce the Wearside club lost only one of their final 11 league matches of the season and going unbeaten in their final six to surge to safety.
A dramatic victory over Chelsea put them in pole position to survive and they sealed their Premier League status with a 3-0 win over Everton on Wednesday, before drawing 2-2 at Watford in Sunday's season closer.
Watmore, who has scored four goals in 25 appearances for the club this season since making his top-flight debut in August, believes the impact Allardyce has had on the club has been immeasurable and admitted his gratitude to the manager for given him repeated first-team opportunities.
The 22-year-old told Sky Sports: "He's been fantastic, on a personal level for me and also the team level. He's given me a lot of opportunities and done a lot on my game with all the coaches, so I've really enjoyed that.
"Then obviously on the team level you can see the difference he's made. I think it's one loss in 11 or something, and we just look a lot more solid. We could have turned some of those draws into victories as well.
"If we can do that - and I'm sure we can - then things are looking bright and hopefully we can keep that together."
Sunderland will now look ahead and hope that with a full season under Allardyce they can avoid the trauma of going through yet another relegation battle next season.