The League One club more than held their own for much of the game at White Hart Lane on Wednesday until Andros Townsend edged the hosts ahead with a 74th-minute penalty.
The winger stepped up after referee Neil Swarbrick had penalised Jay McEveley for handball but Pochettino knows that the tie is far from over.
"It was a tough game," the Tottenham boss told reporters. "Now we go to Sheffield with a victory but it will be tough up there.
"The first half was difficult to create chances. It was a good test.
"It's important to understand what we're up against. We need to go to Sheffield to win."
A full house at Bramall Lane for the return fixture on January 28 will certainly provide Spurs with plenty about which to think but Ryan Mason believes that the north Londoners have the class to cope with anything thrown at them.
The young midfielder remarked: "It was a difficult game. They came with a gameplan and did well. We're happy to go there with a lead.
"We're confident going into the second leg. We kept a clean sheet tonight and we'll go there to win."