The Lotus driver was the only man to complete a 66-lap run, which included one 24-lap stint in which his pace rarely dipped below the 1m29s mark.
Sauber driver Hulkenberg said that stint in particular was striking, particularly given how his own long-run simulations went.
"The Lotus has been very good," Hulkenberg told reporters at Barcelona on Thursday night.
"We didn't do the same programmes, and his fuel would have been down by then so you can't tell [fully], but that [wasn't] a bad effort.
"From what I can remember they were good here last winter as well in terms of tyre life and consistency.
"From how my own tyres felt, [Grosjean's stint] wasn't bad."
Hulkenberg insisted however that there was no ground for worry given how specific conditions at Barcelona have proved this week.
"I'm not really concerned about it. Next week we will be here and maybe it is warmer, maybe the track picks up again. Maybe we have some new parts to try out for Melbourne," he said.
"So far we have had four quality days, the target is to have two more next week.
"In Melbourne we will see how it is but I'm not going to break my brain now."
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