The visitors finished the day on 310-3 with England’s Test captain (94) adding 182 for the third wicket with Gary Ballance (120 not out).
“We are delighted,” said Root.
“It was quite hard graft on a slow wicket and a soft ball made it quite difficult.
“It was a very attritional sort of cricket.
“Looking at the board now, you’d like to think with the batting we’ve got left we’re more than capable of going on and getting past 400 to put them under real pressure when it comes to bowling.
“There were a lot of fielders in front of the bat, and it was just about grinding them down.
“More than anything not letting your ego get in the way of scoring at a certain rate and making sure (today) is the day to put pressure on them.
“We’re in that position now where we can do that, and hopefully Gary can make this big hundred count.
“I’m stood here right now disappointed that I didn’t make that score into a 150 plus.
“But it has been great to come back and contribute.
“There has been a couple of occasions over the last few years where I’ve not managed to.
“It’s really pleasing to get a few runs and put us in a position now where we can hopefully make a 400 plus score.”
Hampshire first team manager Adi Birrell commented: “It was a long day for us.
“It looked like a really good batting wicket so I was really concerned at the toss.
“They have a good batting side and their two Test batsmen got in and went quite bit. It was a toil.
“I am really proud of the way the guys fought in the last session.”