Hamilton dropped behind Max Verstappen at the first corner of last weekend's race in Barcelona but recovered to record a third victory from four races to make his best start to a Formula 1 campaign.
Although unable to pass Verstappen before stopping for a second time, on fresh rubber Hamilton had no such problems after cruising up to the gearbox of his championship rival, finally making his move with six laps remaining.
In a Mercedes video, Shovlin explained: "The conditions were quite different to those that we had seen in free practice but from the runs that Lewis and Max were doing, we could see that the tyres were dropping and they were dropping a bit more than we expected from our pre-event simulations, where we actually thought a one-stop and a two-stop were very close in terms of performance.
"What we could start to see when we put that degradation and put it into our linear strategy tools was that the two stop was now coming out as a clear winner and the point that we actually decide to trigger the stop, well, really, that's the point where we are talking about calling the driver in and getting the pit crew out.
"But when we got into that second stint that was when we really started seriously thinking about making this happen. We are checking the degradation, so we are making sure that Lewis can actually catch up on that other set, we are making sure that when he does catch Max he has got the pace to be able to overtake him and for a lot of that stint, we were actually just reviewing the optimum lap.
"We knew it was somewhere in that [lap] 40 to 43 region and if we go too early, by the time he catches Max, his tyres haven’t got enough grip to be able to pass, if we go too late we haven’t given him enough laps remaining in the race to be able to actually catch and attack.
"So, as I said it was really just a case of finetuning, but the decision isn’t taken until we decide to actually pull the trigger and go for it.”
After the race, Hamilton commented he felt he could have passed Verstappen on track before pitting a second time but chose to trust his team and box for a second fresh set of medium Pirelli tyres.
As for why Mercedes chose to pit Hamilton rather than allow the race to play out uninterrupted, Shovlin added: "I think with the fresher tyres that were on Lewis's car it would have probably happened at some point because Max would have started to get pretty significant degradation towards the end of the race.
"However, if we had done that you then have the disadvantage almost of being the race leader and Max could have done to Lewis what we did to him.
"So, he could have converted to a two-stop as soon as Lewis had overtaken him, and this might have happened around the point that we decided to pull the trigger on the extra stop anyway."
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