Sehwag smashed a monumental 309 and Tendulkar hit 194 not out to lift India to 675 for five when stand-in captain Rahul Dravid declared an hour before close on the second day of the first Test in Multan.
"It is obviously very disappointing to have come so close and not be able to achieve it," said Tendulkar, whose 33rd Test hundred left him only one short of former Indian captain Sunil Gavaskar's world record tally of 34.
"I was aware the declaration was round the corner but I was surprised when it happened.The plan was to give Pakistan an hour to bat and I thought we will get a few overs more to go for it. But once the declaration was made, there was nothing I could do."
Dravid is leading India in only his second Test following a back injury suffered by skipper Sourav Ganguly in the preceding one-dayers which India edged 3-2.
Tendulkar put aside his personal disappointment to pay tribute to Sehwag, who surpassed the previous Indian record of 281 by Venkatsai Laxman against Australia in Kolkata in 2001.
"It is a great moment for Indian cricket," he said of Sehwag's feat.
"A 300-man was needed in India because almost every other country has one. It may have taken a long time to come, but it is better late than never.It was such a fabulous knock, watching it at the other end was thrilling.Such kind of strokeplay is rare. I thought he would go for Mathew Hayden's world record of 380 after he crossed the 300-mark."
"I think Pakistan made such a lifeless wicket because our bowlers had done so well in the One-day series. The batters have done their job, now it is up to the bowlers to go for it, but we must back them with good fielding. The pitch will get slower over the next three days, but I do not think it will trouble anyone much."
Sehwag, who publicly stated on Sunday he would go for 300 after ending the first day on 228, said he was a happy man.
"I was ready for 300 since the morning because I had slept well," the 25-year-old Delhi opener said.
"I am delighted to achieve the highest score for India. Maybe I am a bit disappointed at missing Hayden's record, but I will settle for a 300 any day. This innings will increase my confidence when I bat the next time. I hope I can continue the same form for the rest of the series."
India, who have never won a Test match in Pakistan, are visiting their neighbours for a full tour for the first time since 1989.