The 44-10 win sees Ireland go top of Pool D and they can seal a quarter-final spot if they beat Italy at the Olympic Stadium next Sunday.
"Next week is the pivotal week. It's pressure for us and pressure for Italy," said Schmidt.
"That is why people come to a World Cup - they want to see how teams respond."
After facing Italy, Ireland complete their pool fixtures with a match against France on 11 October.
"For us it starts in earnest now, because we know we can qualify if we win next weekend," added Schmidt.
"The game against France just decides who we play in the quarter-final if we can win next week.
"Italy, after a win and a loss, need to win to qualify. It becomes a last-16 game for us."
Ireland must wait to find out if Rob Kearney will be fit after he was injured in scoring the fifth try shortly after coming on as a substitute.
"Rob was involved in a high-speed play after coming on the pitch and just after scoring the try he's jarred himself," Schmidt added.
"We hope it is not too much but the next 24 to 48 hours will tell if he has done anything telling for next week."
Losing Kearney would be a setback for Ireland, but several players impressed in a dominant performance against Romania.
Schmidt made 12 changes with Italy and France in mind, but his altered line-up showed few signs of weakness, scoring six tries, including four in the second half.
Tommy Bowe and Keith Earls crossed the line twice each, before Kearney and Chris Henry added two more late on, and Simon Zebo also staked a claim with an impressive display at full-back.
"There were a number of players who performed really well and will create a big of selection headache for Italy," Schmidt said.
Ireland's World Cup campaign "starts in earnest now" after Sunday's convincing bonus-point victory over Romania, according to coach Joe Schmidt.