O'Sullivan was replaced by Declan Kidney in 2008 having presided over an abysmal World Cup and Six Nations.
Now working as the Eagles' head coach, O'Callaghan fears O'Sullivan's in-depth understanding of Ireland's players gleaned from his seven year-reign at Lansdowne Road.
"Eddie knows every one of us really well. We know he will exploit any weaknesses in our side," he said.
"He puts in so much time into analysing opposition teams.
"Eddie was an incredible coach and I learnt so much from him. I liked him too.
"There were never any grey areas, just black and white. He never shied away from telling you what was required. Personally I found that brilliant."
O'Callaghan believes the date of the match - September 11 - will give the Americans added motivation to register a shock victory at Stadium Taranaki.
"Playing the USA on the 10th anniversary of the September 11 attacks and against our old coach, it will be a big occasion," said the Lions lock.
"We expect the USA to be fired up for this match."
After slumping to four successive defeats in their warm-up internationals, Ireland are sure to return to winning ways next weekend.
The key fixtures in Pool C are against Australia in Auckland on September 17 and Italy on October 2.
The Wallabies, who were crowned Tri Nations champions last month, are in fine form while Italy will fancy their chances of toppling Ireland having viewed their recent results.
"It's a tough pool. The Russians looked strong in the Churchill Cup while Italy are our most physical game in the Six Nations," said O'Callaghan.
"Australia are playing very well. We know all about tough pools in the Heineken Cup and it's about playing knockout rugby every week."
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