Championship round-up: Middlesbrough's promotion hopes still alive
Marvin Sordell's goal, his first in 19 matches, looked as if had secured victory for second-tier basement club Burton before Assombalonga equalised in the last minute of the match.
The point saw Middlesbrough stay sixth in the Championship table -- the final play-off position.
Only the top two teams at the end of the regular season are guaranteed promotion to the Premier League, with leaders Wolves and nearest pursuers Cardiff well in front of the chasing pack.
The next four sides will then be involved in play-off games, culminating in a Wembley final, to determine which one gets the third and last promotion place.
Brentford remained in the play-off hunt with a 1-0 victory at Bristol City secured by substitute Neal Maupay's goal 10 minutes from time.
Earlier, Wales international Tom Lawrence's free-kick ended Derby's eight-match winless run with a 1-0 victory over fellow play-off chasers Preston.
"This was a massive result for us," said Derby manager Gary Rowett. "We needed this win."
Preston had missed a glorious chance to take the lead in the first half when Alan Browne's penalty hit the post.
Millwall kept their play-off push going with a 2-2 draw at Ipswich but manager Neil Harris was frustrated despite the south London club extending their unbeaten league run to 14 games.
Jake Cooper gave Millwall a first-half lead only for two goals in as many minutes from Martyn Waghorn to turn the tide in Ipswich's favour.
George Saville, however, drew Millwall level on the hour mark at Portman Road and the Lions then surged forward in search of a winner only for Ipswich to hold out.
"I'm quite frustrated, I've got to be honest," said Harris. "I think Ipswich made the game what it was, a counter-attacking game that was very open.
"Sometimes when the game's like that and it's going to be who scores the most, you've got to make sure you score more than the opposition."
QPR and Norwich were once mainstays of the top flight but neither looks as if they will be promoted back to the big time this season.
But there was a reminder of times past for Rangers fans as they enjoyed a 4-1 win at home to Norwich.
After Ryan Manning's own goal gave Norwich the lead, Matt Smith set up an equaliser for Massimo Luongo before heading the west London club in front at Loftus Road.
Ebere Eze made it 3-1 before Manning added another goal late on.
In other Championship action later on Monday, second-placed Cardiff can equal a club record nine successive victories if they beat Sheffield United away.
Cardiff boss Neil Warnock -- whose side are seven points clear of third-placed Fulham -- is chasing an English managerial record eighth promotion.