The Italian, set to return to his former club for the first time since his Baggies exit, was speaking about the match that decided Andre Villas-Boas's demise as Blues manager.
Di Matteo, who was then assistant to the Portuguese, was immediately appointed caretaker following a training-ground meeting with owner Roman Abramovich, director Eugene Tenenbaum and chief executive Ron Gourlay.
When asked if he had been bracing himself for a Stamford Bridge departure, Di Matteo said: "I did, yeah, quite frankly. It was a very emotional day, that day, for us."
The revelation came as he marked 257 days in charge of Chelsea, the exact number of days Villas-Boas had spent in the hotseat.
But despite having bagged the Champions League and FA Cup trophies in his first season in charge, Di Matteo now takes his team to the Hawthorns looking for their first win in four league games.
"You need to put things into perspective," the former MK Dons boss added.
"We're in good shape, the players are in good spirit. We need to keep going on and try to get the win.
"We've shown our character many, many times. It's not just a test of character. When we play well and manage to do so in a game, we can win games."
And regarding his controversial dismissal in February 2011 at West Brom, he said: "I learned a lot of things - which people to trust, who not to trust.
"I'm certainly a better coach and manager now from the experience I had in the
past, and the experience I had here as an assistant and now a manager working with these players."