David Moyes saluted West Ham's unlikely FA Cup saviour Pablo Zabaleta after the veteran's first goal in almost three years helped defeat League One Gillingham.
Second-half goals from 34-year-old defender Zabaleta and fellow substitute Pablo Fornals secured a 2-0 win and a place in the fourth round.
Moyes, unlike many of his fellow Premier League managers, named his strongest available team but Gillingham still threatened an upset during a one-sided first half.
However, the visitors were a different side after the break to ensure they avoided a giantkilling.
Moyes, who has two wins from two matches since replacing Manuel Pellegrini at the Hammers' helm, said: "I knew that was going to be hard.
"It was a really tough game. It took us to the second half to get the ball down and show a bit of composure. I'm really pleased with the players' resilience and character.
"I felt in the first half every time the ball came to us we were slashing at it. Zabaleta gave us some balance and passed it well.
"It was his first goal in about 75 games, and he came in and said to the others, 'I've had to bail you out again'!
"But his professionalism is incredible, he's been a really good player, but like us all as you get older you slow down a bit.
"Obviously getting through is key and I really felt the players stuck at it. I've only been here a week but we've got two clean sheets, six goals, and there's a feeling that there's a bit of a spirit starting to grow among them.
"The supporters want a cup run and we'll do our best to give them one."
It may have been the most expensively-assembled team to run out at the Priestfield Stadium, but reputations counted for little in the opening stages and Lukasz Fabianski had to make smart saves from Connor Ogilvie and Brandon Hanlan.
West Ham did not manage a meaningful effort on goal during a tough first half which got worse shortly before half-time when wing-back Ryan Fredericks pulled up mid-sprint with a hamstring injury, forcing Zabaleta's introduction.
Moments after the interval, £45million record buy Sebastien Haller skied a one-on-one with goalkeeper Jack Bonham and then hit the inside of a post.
The goal eventually arrived in the 73rd minute, Felipe Anderson freeing Arthur Masuaku to reach the byline and pull the ball back.
The ball had too much pace for Fornals but it skidded through to Zabaleta, whose shot took a deflection on its way past Bonham for his first West Ham goal.
Gillingham mounted a late rally, but they were caught on the break in stoppage time when Anderson teed up Fornals to leave the home defenders on their knees.
Gills manager Steve Evans said: "I'm pleased with the first half, we were by some distance the dominant side but you have to have a goal to show for it.
"We said more of the same but you knew there was going to be a reaction and Moyesy got a reaction. They were better than us in the second half, so no complaints."