End-to-end action now.

Exeter turn over the Ulster lineout and attack, but again as they get into the red zone their handling lets them down and they drop the ball.

Now Ulster punish them with a kick into touch deep within the visitor's 22.

Exeter break clean through the Ulster defence and Stephen Varney finds himself with one man to beat.

The Italian international passes to his right, but it is a loopy effort and goes beyond the grasp of his team-mate.

Ulster escape.

TMO check here for a potential high tackle on Ulster's Juarno Augustus

But the referee can see no clear infringement and we return to an Ulster scrum 10 metres inside the home team's half.

Ulster win a penalty and kick to within five metres of the Exeter line.

Now the hosts have a chance to force the issue.

Ulster steal the line-out and Nathan Doak clears brilliantly to touch inside the Exeter half

The hosts are pinged for a high tackle just inside their own half so it is a penalty to the Chiefs.

They opt to kick to the corner and do a good job of it.

Ethan McIlroy replaces Jacob Stockdale at the break for Ulster.

Ulster kick long to get the second half under way here in Belfast. Only one of these teams will be still standing in 40 minutes time.

A reminder of what's at stake in today's match...

The winner will meet either Montpellier or Dragons in the final in Bilbao on Friday, 22 May for the Challenge Cup trophy.

Andy Gray
BBC Sport NI at the Affidea Stadium

As to be expected in a European semi-final, this is an awfully tense affair.

Despite being down to 14 men for the final quarter of the half, Ulster really kicked on and deserved to retake the lead through Nathan Doak.

A big 40 minutes to come for both sides.

Image source, Getty Images

Ulster hit the sheds with a narrow lead, but all to play for after the break.

Nathan Doak lands the penalty and that is the end of an eventful opening half.

Penalty to Ulster on the edge of the Exeter 22.

After leaving empty-handed with their previous penalties, it is no surprise Nathan Doak opts for the kick this time.

Exeter win a penalty at the scrum but fail to find touch, Ulster back on the attack!

But the ball is held up over the line.

Disappointment for Ulster, but they are awarded a penalty five metres from the line.

However, they knock the ball on! Scrum Exeter.

Ulster back on the attack 10 metres out from the Chiefs' line.

Andy Gray
BBC Sport NI at the Affidea Stadium

The crowd knew immediately that Jacob Stockdale would be in bother for that one.

There was an anxious hush as they waited for the verdict from Pierre Brousset, and I don't think the Ireland wing can have too many complaints there.

Image source, Getty Images

Jacob Stockdale is off for 10 minutes after a high hit on Exeter winger Immanuel Feyi-Waboso, who has gone off for a head injury assessment.

The Chiefs are now attacking deep within Ulster territory.