"First of all I'm disappointed with the result, but proud of the performance. I said to the players that when we're so good like we were at times in the first half, we have to be clinical. We had three good chances to score."
At the other end, when things aren't going for you, it really kicks you when your down. There was a terrific save from Ben Amos from a point-blank header then the ball clips the bar when were just about to clear it, and lands at Dwight Gayle's foot. You can't do anything with things like that. The second goal goes through Mahlon Romeo's legs, if it hits his shin pad it goes wide.
The Lions boss was happy with the reaction of his side after Wednesday's disappointing performance at QPR.
"I'm pleased with the players. The first half at QPR wasn't good enough, and you can point to not scoring goals and that we've had some poor halves of football. But today, we had some good performances from individuals, there was some real positive in the character and belief of the team.
Harris is also confident his team just need one win to get themselves going.
"Once we get that first bit of luck or performance that wins us a game, there will be plenty more to come.
"I thought our shape was excellent, if anyone had questioned the belief of this Millwall team that we have come to love over the last three and -a half years, the first hour today showed it's all there."
Harris made four changes to his starting lineup and praised the leadership of Byron Webster to made his first league appearance after a long injury lay off.
"Players like Byron Webster who has not played a league game for us for 12 months, played really well today. I saw some real leadership on the pitch in the group and some really good football as well. We just need to be a bit more clinical in the final third.
'The four changes were due to playing three games in seven days. There was a bit of illness in the group and just to freshen up the team. We were in a game today that needed lots of energy and freshness."
Jiri Skalak made his first start of the season and Tom Bradshaw was partnered with Steve Morison up front and Harris praised the efforts of the duo.
"Playing well with and without the ball, and I thought Jiri Skalak and Tom Bradshaw both did really well. Jiri is a crosser of the ball, and although there was a bit of rustiness against a good West Brom side, we also saw some real moments of quality from both wide players today."
We are now entering a period of two games a week until the International break and the Lions boss believes it is important that his side build momentum going into that break.
"I made it clear to the players that we need to focus only on the next game rather than looking to far ahead. We have three home games in four now. It's about building momentum in those matches, on the back of four good performances at The Den.
"Win, lose or draw on Tuesday I'm looking for a Millwall performance to take into Saturday when the result becomes a priority against Sheffield United.
Harris also paid tribute to the 'outstanding' support of the fans at the Hawthorns.
"We're in a horrible run of games, the worst run while I've been in charge, and the supporters were absolutely top drawer towards myself and the players. I never take it for granted, I thought they drove the team on, and I appreciated at the end when nearly everyone of them stayed to appreciate a good performance. I was shocked when I looked over and saw the amount that had travelled.
"I hope they see enough in the group, the board and the staff that we've had a great three and a half years, and that we need to stick together. I thought their backing was outstanding."