However, Kostyuk recovered to serve out the match and let a huge roar of relief.
Afterwards Boulter put her struggles down to the tweaks she has been trying to make to her serve.
“I’m trying to find rhythm and don’t fully commit to the serve I’m going for,” added Boulter, who was broken four times.
“At this level, putting the serve in the court is not going to get it done.
“Otherwise, on the court, I matched Marta well and returned decently well. Considering my form it was a relatively competitive match.”
British number four Jones fought through qualifying to make her debut in the main draw, but was ground down by 59th-ranked Lys’s solidity in a 6-0 7-5 defeat.
Jones, 24, has climbed to 86th in the rankings after winning two titles on the second-tier WTA 125 Tour post-Wimbledon.
However, the way she was moved around by Lys in the rallies – and forced into mistakes – was a reminder of the level she needs to find to go even higher.
Harris, 30, moved into the main draw after losing in the final qualifying round because of withdrawals and acquitted himself well against 2021 semi-finalist Auger-Alissiame.
While he lost 6-4 7-6 (10-8) 6-4, the British number six pushed his opponent in each set and things might have turned out differently had he converted any of his two set points in the tie-breaker.
