Thiam, who has been meeting UK investors this week to explain the merits of the blockbuster deal, appears to be winning over skeptics, they said.
"We asked him to justify the deal to us and he made a pretty good fist of it," said one head of equities who met with Thiam.
"Coming out of it, we were a little more positive than we thought we would be. It is a bit of an opportunity for Pru; a real catch and it will make them very strong indeed. All in all, there is an argument for (the deal)."
Another large investor who also met Thiam added: "The key message was that AIA will make a lot more money under Prudential's ownership.
"The AIA business has much poorer margins than the existing Pru business so there is some credibility in that argument. Overall, we felt what they are doing does have some merit."
AIG shares were up nearly five percent in pre-market trade shortly after Reuters reported growing backing for the deal.
Investors said Thiam told them that removing inefficiencies in AIA's operations would result in strong revenue synergies and said he reassured them on the price tag, which some have said was too high.
"Pru's Asian operations are very efficient and as a result their margins are very high...AIA is not as productive. Get the two together and you can make a case for increasing that productivity and justifying what ostensibly looks like a pretty high valuation," said the head of equities.
"Pru sees some $770 million of revenue synergies coming through this increased agency productivity. This isn't a company that is going to make $500 million of new business, it can in time make $2 billion on new business and so you can justify the price."
Thiam also told investors AIA has been on his radar since September 2008, when he was Prudential's chief financial officer.
"We thought this is quite important because they do know the operations better than we may have thought," added the head of equities.
However, some investors are yet to be convinced.
"Tidjane is relatively unknown -- he's only been there for nine months and therefore for an unknown to be asking for this kind of money, people are reasonably skeptical," one said.
"There is also a bit of worry that they may redomicile -- we may end up buying all the stock and they may take off to Hong Kong," he added.