Watson opened the batting for the Australians in their opening tour match against Somerset in Taunton on Wednesday, and that's how it will stay for the big English summer ahead.
An extraordinary late flurry of wickets in which Australia's quicks took six wickets for no runs in the space of 29 balls saw the tourists fight back from a worrying position to bowl Somerset out for 320 on day one.
Watson and Ed Cowan then got through one over for the Australians to finish 0-2 at stumps.
Fast bowlers Mitchell Starc (4-33) and James Pattinson (4-56) starred with the ball but the talking point after the match was Watson.
The 32-year-old hasn't opened in a Test match since November 2011 in South Africa, despite it being his preferred position.
In various other roles in the order he's struggled for consistency but Lehmann has given Watson an assurance he'll lead off for Australia in the first Test against England at Trent Bridge in two weeks.
"Yes. He'll be opening for us," Lehmann said.
"That's where we want him to bat and he's done really well for us there.
"We're quite keen for him to open and to have a big part in the Ashes and obviously make a lot of runs for us and start the innings up well."
Watson didn't bowl on Wednesday, but Lehmann said he would roll the arm over in Australia's second tour game against Worcestershire next week.
With the bat, Watson averages 43 opening compared to his overall career average of 35, while his two Test centuries have also come at the top of the order.
Cowan and recalled veteran Chris Rogers will now fight it out for the right to partner Watson in the first Test.
Rogers has the runs on the board in English county cricket, but Cowan has the luxury of playing this match in Taunton.
Lehmann said he wouldn't speculate on other positions in his order, but made it clear he was looking for runs.
"If you perform you'll have a chance to play in the first Test. We want to give everyone in our squad the opportunity to perform well in the tour games," he said.
Lehmann was satisfied captain Michael Clarke's back pulled up well in his first day's cricket in three months.
Clarke showed no problem with movement when he took a spectacular juggling catch to his left off the bowling of Nathan Lyon to remove Nick Compton for 81.
Compton combined in a 170-run second wicket stand with Chris Jones, who made his maiden first-class century of 130.
Australia's bowlers struggled for answers in the first two sessions, showing there's a lot of improvement needed before the first Test.
But they roared home with the second new ball.
Starc, who recently had ankle surgery, looked short of a gallop for most of the day, but bounced back brilliantly with some menacing in-swingers in the final session.
James Faulkner (1-70) also had his strong moments, and spinner Lyon (1-75) showed some encouraging signs.
Peter Siddle (0-62) looked rusty and bowled a fraction too short.
"We got it right with the second new ball. I thought we didn't get it right with the first one. So that's something we've got to work on," Lehmann said.
"All in all a good result at the end of the day."